[424B5] ATAI Life Sciences N.V. Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

ATAI Life Sciences N.V. is offering 23,725,000 common shares at $5.48 per share, a primary raise totaling $130,013,000 in gross proceeds. Underwriting discounts are $0.349876 per share, for $121,712,191.90 in proceeds before expenses; the company estimates net proceeds of about $121.2 million. The underwriters have a 30‑day option to buy up to 3,558,750 additional shares.

ATAI intends to use proceeds to advance clinical development, and for working capital and general corporate purposes. Shares outstanding will be 235,969,597 after the offering (or 239,528,347 if the option is exercised), versus 212,244,597 outstanding as of June 30, 2025. ATAI preliminarily expects $114.6 million in cash, cash equivalents and short‑term investments as of September 30, 2025. Recent items include an agreement to issue 105,044,902 shares for the planned Beckley Psytech combination (subject to shareholder approval) and FDA Breakthrough Therapy designation for Beckley Psytech’s BPL‑003.

Insights

Capital markets analyst

Primary equity raise of ~$121M net to fund clinical programs.

ATAI priced a primary offering of 23,725,000 shares at $5.48, yielding $121.7M before expenses and an estimated $121.2M net. A 30‑day underwriters’ option adds up to 3,558,750 shares. This injects cash directly to the issuer for development and corporate purposes.

Post‑offering shares outstanding are listed at 235,969,597 (or 239,528,347 with the option). The excerpt notes preliminary liquidity of $114.6M as of Sep 30, 2025, which, combined with proceeds, supports the pipeline plan. Dilution to new investors is disclosed as $4.41 per share in the dilution section.

Additional context includes the planned issuance of 105,044,902 shares for the Beckley Psytech transaction (subject to approval) and FDA Breakthrough Therapy designation for BPL‑003. Actual impact depends on closing conditions and development progress; timing beyond what’s disclosed is not provided in the excerpt.

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Filed Pursuant to Rule 424(b)(5)

Registration No. 333-290592

PROSPECTUS SUPPLEMENT

(to Prospectus dated September 29, 2025)

23,725,000 Common Shares

We are offering 23,725,000 of our common shares, nominal value €0.10 per share (“common shares”), at a purchase price of $5.48 per share. Our common shares are listed on the Nasdaq Global Market under the symbol “ATAI.” On October 16, 2025, the last reported sale price of our common shares on the Nasdaq Global Market was $5.48 per share.

We are an emerging growth company as that term is used in the Jumpstart Our Business Startups Act of 2012, as amended, or the JOBS Act, and a smaller reporting company as defined under Rule 405 of the Securities Act of 1933, as amended, or the Securities Act, and, as such, are subject to certain reduced public company reporting requirements.

INVESTING IN OUR SECURITIES INVOLVES RISKS. SEE THE “RISK FACTORS” BEGINNING ON PAGE S-11 OF THIS PROSPECTUS SUPPLEMENT AND IN THE DOCUMENTS INCORPORATED BY REFERENCE IN THIS PROSPECTUS SUPPLEMENT CONCERNING FACTORS YOU SHOULD CONSIDER BEFORE INVESTING IN OUR COMMON SHARES.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

			Per Share			Total
Offering price			$5.48			$130,013,000.00
Underwriting discounts and commissions(1)			$0.349876			$8,300,808.10
Proceeds, before expenses, to us			$5.130124			$121,712,191.90

(1)
See the section titled “Underwriting” for a description of the compensation payable to the underwriters.

The underwriters may also exercise their option to purchase up to an additional 3,558,750 common shares from us, at the public offering price, less the underwriting discount, for 30 days after the date of this prospectus supplement.

The underwriters expect to deliver the common shares to purchasers on or about October 20, 2025.

Lead Bookrunner

Jefferies

Passive Bookrunner

Berenberg

Co-Managers
Oppenheimer & Co.			Canaccord Genuity

The date of this prospectus supplement is October 16, 2025.

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ABOUT THIS PROSPECTUS SUPPLEMENT			S-1
TRADEMARKS			S-2
WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE			S-3
PROSPECTUS SUPPLEMENT SUMMARY			S-5
THE OFFERING			S-9
RISK FACTORS			S-11
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS			S-13
USE OF PROCEEDS			S-15
DIVIDEND POLICY			S-16
DILUTION			S-17
MATERIAL TAX CONSIDERATIONS			S-19
UNDERWRITING			S-29
LEGAL MATTERS			S-39
EXPERTS			S-39

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ABOUT THIS PROSPECTUS			1
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS			2
TRADEMARKS			4
WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE			5
THE COMPANY			7
RISK FACTORS			8
USE OF PROCEEDS			9
DESCRIPTION OF SHARE CAPITAL AND ARTICLES OF ASSOCIATION			10
DESCRIPTION OF DEBT SECURITIES			16
DESCRIPTION OF WARRANTS			23
DESCRIPTION OF UNITS			24
GLOBAL SECURITIES			25
SELLING SECURITYHOLDERS			28
PLAN OF DISTRIBUTION			30
LEGAL MATTERS			33
EXPERTS			33

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement is part of a registration statement that we have filed with the Securities and Exchange Commission, or SEC, which became automatically effective upon filing, utilizing a “shelf” registration process, and relates to the offering of our common shares. Before buying any of the common shares that we are offering, we urge you to carefully read this prospectus supplement, the accompanying prospectus and all of the information incorporated by reference herein and therein, as well as the additional information described under the heading “Where You Can Find More Information; Incorporation by Reference.” These documents contain important information that you should consider when making your investment decision.

We provide information to you about this offering of our common shares in two separate documents that are bound together: (1) this prospectus supplement, which describes the specific details regarding this offering and also adds to and updates information contained in the documents incorporated by reference into this prospectus supplement; and (2) the accompanying prospectus, which provides general information, some of which may not apply to this offering. Generally, when we refer to this “prospectus,” we are referring to both documents combined. If information in this prospectus supplement is inconsistent with the accompanying prospectus, you should rely on this prospectus supplement. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in any document incorporated by reference in this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in this prospectus supplement—the statement in the document having the later date modifies or supersedes the earlier statement.

You should rely only on the information contained in or incorporated by reference in this prospectus supplement, the accompanying prospectus and any free writing prospectus that we may authorize for use in connection with this offering. We have not, and the underwriters have not, authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering, in their entirety before making an investment decision.

We are offering to sell, and seeking offers to buy, our common shares only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the common shares in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the common shares and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference in this prospectus supplement were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

When we refer to “atai,” “we,” “our,” “us,” the “Company” and “our company” in this prospectus supplement, we mean ATAI Life Sciences N.V. and its consolidated subsidiaries, unless otherwise specified. When we refer to “you,” we mean the potential holders of the applicable series of securities.

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For investors outside the United States: We have not done anything that would permit the offering or possession or distribution of this prospectus supplement in any jurisdiction where action for that purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus supplement must inform themselves about, and observe any restrictions relating to, the offering of the securities described herein and the distribution of this prospectus supplement outside the United States.

TRADEMARKS

We have proprietary rights to trademarks used in this prospectus supplement that are important to our business, many of which are registered under applicable intellectual property laws. Solely for convenience, trademarks and trade names referred to in this prospectus supplement may appear without the “®” or “™” symbols, but such references are not intended to indicate, in any way, that we will not assert, to the fullest extent possible under applicable law, our rights or the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other companies’ trademarks, trade names or service marks to imply a relationship with, or endorsement or sponsorship of us by, any other companies. Each trademark, trade name or service mark of any other company appearing in this prospectus supplement is the property of its respective holder.

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WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE

Available Information

We file reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information about issuers, such as us, who file electronically with the SEC. The address of that website is https://www.sec.gov.

Our website address is https://atai.com. The information contained on, or accessible through, our website does not constitute part of this prospectus supplement. We have included our website address in this prospectus supplement solely as an inactive textual reference.

This prospectus supplement is part of a registration statement that we filed with the SEC and does not contain all of the information in the registration statement. The full registration statement may be obtained from the SEC or us, as provided below. Documents establishing the terms of the offered securities are or may be filed as exhibits to the registration statement or documents incorporated by reference in the registration statement. Statements in this prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement through the SEC’s website, as provided above.

Incorporation by Reference

The SEC’s rules allow us to “incorporate by reference” information into this prospectus supplement, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is deemed to be part of this prospectus supplement, and subsequent information that we file with the SEC will automatically update and supersede that information. Any statement contained in this prospectus supplement or a previously filed document incorporated by reference will be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or a subsequently filed document incorporated by reference modifies or replaces that statement.

This prospectus supplement incorporates by reference the documents set forth below that have previously been filed with the SEC, but excluding any information furnished to, rather than filed with, the SEC:

• Our Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on March 17, 2025.

• The information specifically incorporated by reference into our Annual Report on Form 10-K from our Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 21, 2025.

• The information in the sections entitled “The Redomiciliation,” “Description of ATAI Delaware Common Stock” and “Comparison of Shareholders Rights Between Netherlands Law and Delaware Law” in our Definitive Proxy Statement on Schedule 14A, filed with the SEC on September 24, 2025.

• Our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2025, and June 30, 2025, filed with the SEC on May 14, 2025 and on August 14, 2025, respectively.

• Our Current Reports on Form 8-K filed with the SEC on January 10, 2025, January 24, 2025, February 13, 2025, April 30, 2025, May 8, 2025, May 21, 2025, June 2, 2025, July 1, 2025, September 23, 2025, September 29, 2025, October 10, 2025 and October 16, 2025.

• The description of our Share Capital contained in our Registration Statement on Form 8-A, filed with the SEC on June 14, 2021 and any amendment or report filed with the SEC for the purpose of updating the description.

All reports and other documents we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the termination of this offering but excluding any information furnished to, rather than filed with, the SEC, will also be incorporated by reference into this prospectus supplement and deemed to be part of this prospectus supplement from the date of the filing of such reports and documents.

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You may request a free copy of any of the documents incorporated by reference in this prospectus supplement by writing or telephoning us at the following address:

Attention: Secretary

ATAI Life Sciences N.V.

Prof. J.H. Bavincklaan 7

1183 AT Amstelveen

The Netherlands

+31 20 793 2536

Exhibits to the filings will not be sent, however, unless those exhibits have specifically been incorporated by reference in this prospectus supplement.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary provides a general overview of selected information and does not contain all of the information you should consider before buying our common shares. Therefore, you should read this entire prospectus supplement, the accompanying prospectus and any free writing prospectus that we have authorized for use in connection with this offering carefully, including the information incorporated by reference into this prospectus supplement, before deciding to invest in our common shares. Investors should carefully consider the information set forth under “Risk Factors” beginning on page S-11 of this prospectus supplement and incorporated by reference to our Annual Report on Form 10-K, our quarterly reports on Form 10-Q and any other documents incorporated by reference into this prospectus supplement.

Company Overview

We are a clinical-stage biopharmaceutical company on a mission to develop highly effective mental health treatments to transform patient outcomes. Founded in 2018, atai emerged from the urgent need for better mental health solutions for patients who are under-served by current treatment options. We are advancing a pipeline of product candidates designed to address the complex nature of mental health disorders. We believe that these investigational compounds have the potential to become rapid-acting, durable, and commercially scalable therapies for mental health patients in need of new treatment options.

Mental health disorders are highly prevalent and estimated to affect more than one billion people globally. The economic burden of these disorders is substantial and growing rapidly. Between 2009 and 2019, spending on mental health care in the United States increased by more than 50%, reaching $225 billion, and a Lancet Commission report estimates that the global economic cost will reach $16 trillion by 2030. While current treatments, such as selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors are well established and effective for certain patients, approximately 65% of patients do not achieve remission of their symptoms after up to four antidepressant treatment trials, translating to a significant unmet medical need.

Since our inception in 2018, we have focused substantially all of our efforts and financial resources on acquiring and developing product and technology rights, establishing our platform, building our intellectual property portfolio and conducting research and development activities for our product candidates within our atai companies that we consolidate based on our controlling financial interest of such entities. We are advancing a pipeline of product candidates designed to address the complex nature of mental health disorders. We believe that these investigational compounds have the potential to become rapid-acting, durable, and commercially scalable therapies for mental health patients in need of new treatment options.

We do not have any products approved for sale and have not generated any revenue from product sales; however, we have recognized revenue from license and research and development arrangements. We have funded our operations to date primarily with proceeds from the sale of our common shares and issuances of convertible notes.

Recent Developments

Beckley Psytech Strategic Combination

We have a strategic investment in Beckley Psytech Limited (“Beckley Psytech”), a private clinical-stage biopharmaceutical company developing two investigational compounds: BPL-003, mebufotenin benzoate, for TRD and alcohol use disorder, and ELE-101, psilocin, for the treatment of major depressive disorder.

In June 2025, we entered into a share purchase agreement (the “SPA”) with Beckley Psytech and certain other parties thereto, pursuant to which we agreed to acquire from the shareholders of Beckley Psytech (the “Sellers”) the entire issued share capital of Beckley Psytech not already owned by the Company by issuing to the Sellers 105,044,902 of our common shares (subject to certain adjustments). The strategic combination with Beckley Psytech is expected to close in the fourth quarter of 2025, subject to approval of the share issuance by the Company’s shareholders and satisfaction of other customary closing conditions. Subject to shareholder approval and the consummation of the strategic combination pursuant to the SPA, Cosmo Feilding-Mellen and Dr. Robert Hershberg are expected to become members of our board of directors following the consummation of such strategic combination.

Corporate Redomiciliation

In August 2025, our board of directors approved a redomiliciation of the Company to Delaware (the “Redomiciliation”). The Redomiciliation is intended to generally improve the Company’s operational and financial

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flexibility and provide for a more efficient corporate structure to achieve strategic and financial goals. As Dutch law does not facilitate a direct change of legal domicile of a Dutch public limited liability company (such as us) to a jurisdiction outside the European Economic Area, the Redomiciliation is anticipated to be effected through a series of transactions occurring in a specific sequence and as a consequence of which, among other things (i) the Company and a newly formed Luxembourg entity (“ATAI LuxCo”) would enter into a cross-border merger, as a result of which the Company would cease to exist and all assets and liabilities of the Company would be transferred to ATAI LuxCo (the “LuxCo Merger”), and (ii) ATAI LuxCo would redomesticate in Delaware, as permitted under Luxembourg law. The Redomiciliation is subject to, among other things, the approval of the LuxCo Merger and related matters by the Company’s shareholders.

Beckley Psytech Breakthrough Therapy Designation

On October 16, 2025, Beckley Psytech announced that the U.S. Food and Drug Administration (the “FDA”) granted Breakthrough Therapy designation (“BTD”) to BPL-003 (intranasal mebufotenin benzoate) for adult patients with treatment-resistant depression (“TRD”). BTD is granted to drugs targeting serious or life-threatening conditions where preliminary clinical evidence suggests that the drug may demonstrate substantial improvement on one or more clinically significant endpoints over existing therapies. BPL-003 is designed to deliver rapid and durable antidepressant effects from a single dose with a short therapeutic experience. The designation follows positive topline results from Beckley Psytech’s Phase 2b core, blinded study of BPL-003 in TRD which showed that a single administration of 8 mg or 12 mg of BPL-003 led to clinically meaningful and statistically significant reductions in depressive symptoms within 24 hours, with effects sustained through the eight-week trial period. Notably, most patients were deemed ready for discharge at the 90-minute post-dose assessment, underscoring the potential scalability of the BPL-003 treatment model and its potential to fit into the established two-hour, in-clinic interventional psychiatry treatment paradigm.

Certain Preliminary Financial Results as of September 30, 2025

Although we have not finalized our full financial results for the three months ended September 30, 2025, we expect to report that we had approximately $114.6 million in cash, cash equivalents and short-term investments as of September 30, 2025.

The information above is based on preliminary unaudited information and estimates for the three months ended September 30, 2025, is not a comprehensive statement of our financial results for this period, and is subject to change pending completion of our financial closing procedures, final adjustments, completion of the review of our financial statements and other developments that may arise between now and the time the review of our financial statements is completed. This preliminary estimate may change and the change may be material. Our expectation with respect to our cash, cash equivalents and short-term investments at September 30, 2025 is based upon management estimates and is the responsibility of management. Neither our independent registered public accounting firm nor any other independent auditor has conducted an audit or review of, and does not express an opinion or any other form of assurance with respect to, these preliminary estimates. Our actual results for the three months ended September 30, 2025, will not be available until after this offering is completed.

Summary Risk Factors

Our business is subject to numerous risks and uncertainties that may have a material adverse effect on our business, financial condition or results of operations. These risks are more fully described below. These risks include, among others:

• We are a clinical-stage biopharmaceutical company and have incurred significant losses since our inception. We expect to incur losses for the foreseeable future and may never be profitable;

• Our limited operating history may make it difficult for you to evaluate the success of our business and to assess our future viability;

• If we are unable to obtain funding when needed and on acceptable terms, we could be forced to delay, limit or discontinue our product candidate development efforts;

• Raising additional capital, such as through future sales and issuances of our common shares or rights to purchase common shares, including pursuant to our equity incentive plans, may cause dilution to our shareholders, restrict our operations or require us to relinquish rights to current product candidates or to any future product candidates on unfavorable terms;

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• Our product candidates are in preclinical or clinical development, which is a lengthy and expensive process with uncertain outcomes. We cannot give any assurance that any of our product candidates will be successfully developed and/or receive regulatory approval, which is necessary before they can be commercialized;

• Because we have multiple programs and product candidates in our development pipeline, in addition to our continued business development activities, we may, and have in the past decided to, expend our limited resources and allocation of capital to pursue a particular product candidate over other product candidates that may ultimately have been more profitable or for which there may have been a greater likelihood of success, which may adversely affect our future revenues;

• We may not achieve our publicly announced milestones according to schedule, or at all;

• We currently rely on qualified therapists working at third-party clinical trial sites to administer certain of our product candidates in our clinical trials, and we expect this to continue upon approval, if any, of our current or future product candidates. If third-party sites fail to recruit and retain a sufficient number of therapists or effectively manage their therapists, our business, financial condition and results of operations would be materially harmed;

• Research and development of drugs targeting the central nervous system, or CNS, is particularly difficult, and it can be difficult to predict and understand why a drug has a positive effect on some patients but not others, which may reduce the likelihood our product candidates are ultimately approved and therefore may have a material adverse effect on our business and operating results;

• The production and sale of our product candidates may be considered illegal or may otherwise be restricted due to the use of controlled substances, which may also have consequences for the legality of investments from foreign jurisdictions and therefore we may not be successful in commercializing our product candidates in such jurisdictions, which will adversely affect our business, financial condition and results of operations;

• We face significant competition in an environment of rapid technological and scientific change, and there is a possibility that our competitors may achieve regulatory approval before we do or develop therapies that are safer, more advanced or more effective than ours, which may negatively impact our ability to successfully market or commercialize any product candidates we may develop and ultimately harm our financial condition;

• We rely on third parties to assist in conducting our clinical trials and some aspects of our research and preclinical testing, and those third parties may not perform satisfactorily, including failing to meet deadlines for the completion of such trials, research, or testing;

• If we are unable to obtain and maintain sufficient intellectual property protection for our existing product candidates or any other product candidates that we may identify, or if the scope of the intellectual property protection we currently have or obtain in the future is not sufficiently broad, our competitors could develop and commercialize product candidates similar or identical to ours, and our ability to successfully commercialize our existing product candidates and any other product candidates that we may pursue may be impaired;

• Third parties may claim that we are infringing, misappropriating or otherwise violating their intellectual property rights, the outcome of which would be uncertain and may prevent or delay our development and commercialization efforts;

• Our business is subject to global financial and economic conditions and geopolitical events, including overall market volatility in the global financial markets, as well as political, trade and regulatory developments;

• Our business is subject to economic, political, regulatory and other risks associated with international operations;

• Our future success depends on our ability to retain key employees, directors, consultants and advisors and to attract, retain and motivate qualified personnel;

• A pandemic, epidemic, or outbreak of an infectious disease may materially and adversely affect our business, including our preclinical studies, clinical trials, trial sites, third parties on whom we rely, our supply chain, our ability to raise capital, our ability to conduct regular business and our financial results;

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• If we fail to maintain an effective system of disclosure controls and internal control over financial reporting, our ability to produce timely and accurate financial statements or comply with applicable regulations could be impaired;

• If you purchase our common shares sold in this offering, you will experience immediate and substantial dilution in the net tangible book value of your common shares. In addition, we may issue additional equity or convertible debt securities in the future, which may result in additional dilution to you;

• We have broad discretion in the use of the net proceeds from this offering and may not use them effectively;

• The market price of our common shares may be adversely affected by market conditions affecting the stock markets in general, including price and trading fluctuations on The Nasdaq Global Market;

• Future sales, or the possibility of future sales, of a substantial number of common shares could adversely affect the price of such securities;

• Interim, “top-line,” and preliminary data from clinical trials that we or Beckley Psytech announce or publish from time to time may change as more patient data become available or as additional analyses are conducted, and as the data are subject to audit and verification procedures that could result in material changes in the final data;

• Failure to complete the proposed strategic combination with Beckley Psytech could negatively impact our share price; and

• The expected benefits of the Redomiciliation may not be realized, and the Redomiciliation may not be implemented or may not be implemented in a timely manner.

Corporate Information

The statutory seat of ATAI Life Sciences N.V. is in Amsterdam, the Netherlands. Our office address and our principal executive office is located at Prof. J.H. Bavincklaan 7, 1183 AT Amstelveen, the Netherlands, and our telephone number is +31 20 793 2536. Our website address is https://atai.com. The information contained on, or that can be accessed from, our website does not form part of this prospectus supplement. References to our website address do not constitute incorporation by reference of the information contained on the website, and the information contained on the website is not part of this prospectus supplement or any other document that we file with or furnish to the SEC.

Implications of Being an Emerging Growth Company

We are an emerging growth company, as defined in the JOBS Act. We intend to rely on certain of the exemptions and reduced reporting requirements provided by the JOBS Act. As an emerging growth company, we are not required to, among other things, (i) provide an auditor’s attestation report on our system of internal controls over financial reporting pursuant to Section 404(b) of the Sarbanes-Oxley Act, and (ii) comply with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial statements (auditor discussion and analysis). We have implemented certain accounting standards ahead of their required adoption dates, as the JOBS Act does not preclude an emerging growth company from adopting a new or revised accounting standard earlier than the time that such standard applies to private companies. We have elected to use the extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that (i) we are no longer an emerging growth company or (ii) we affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result of these elections, the information that we provide in this prospectus supplement may be different than the information you may receive from other public companies in which you hold equity interests. In addition, it is possible that some investors will find our common shares less attractive as a result of these elections, which may result in a less active trading market for our common shares and higher volatility in our share price.

We will remain an emerging growth company until the earliest to occur of: (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of our initial public offering, or December 31, 2026, (b) in which we have total annual gross revenues of $1.235 billion or more, or (c) in which we are deemed to be a large accelerated filer under the rules of the SEC, which means the market value of our outstanding common shares held by non-affiliates equals or exceeds $700 million as of last business day of our most recently completed second fiscal quarter, and (2) the date on which we have issued more than $1.0 billion in nonconvertible debt during the previous three years.

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THE OFFERING

Common shares offered by us

23,725,000 common shares.

Common shares to be outstanding after this offering

235,969,597 common shares (or 239,528,347 common shares if the underwriters exercise in full their option to purchase additional common shares).

Option to purchase additional common shares

We have granted the underwriters a 30-day option to purchase up to 3,558,750 additional common shares at the public offering price less the underwriting discounts and commissions.

Use of proceeds

We intend to use the net proceeds of this offering, together with our existing cash, cash equivalents and short-term investments, to advance the clinical development of our product candidates and programs, as well as for working capital and general corporate purposes. See the section entitled “Use of Proceeds” on page S-15 of this prospectus supplement.

Risk factors

See “Risk Factors” beginning on page S-11 of this prospectus supplement and the other information included in, or incorporated by reference into, this prospectus supplement for a discussion of certain factors you should carefully consider before deciding to invest in our common shares.

Nasdaq Global Market symbol

ATAI

The number of our common shares to be outstanding after this offering is based on 212,244,597 common shares outstanding as of June 30, 2025, and excludes:

• 10,743,021 common shares issuable upon the exercise of options outstanding under our 2020 Employee, Director and Consultant Equity Incentive Plan, or the 2020 Plan, as of June 30, 2025 at a weighted-average exercise price of $4.90;

• 37,822,494 common shares issuable upon the exercise of options outstanding under our 2021 Incentive Award Plan, or the 2021 Plan, as of June 30, 2025 at a weighted-average exercise price of $2.76;

• 40,454,775 common shares reserved for future issuance under our 2021 Plan as of June 30, 2025;

• 257,419 common shares reserved for future issuance under our Hurdle Share Option Program, or the HSOP, as of June 30, 2025;

• 10,877,216 common shares issuable upon the exercise of pre-funded warrants;

• 6,185,904 common shares issuable upon the conversion of convertible notes, and such common shares were issued on September 17, 2025 and October 7, 2025 in connection with the conversion of such convertible notes;

• 18,264,840 common shares issuable pursuant to subscription agreements, dated July 1, 2025, between us and the investors party thereto, and such common shares were issued on August 14, 2025 in connection with the closing of the sale of such common shares pursuant to the subscription agreements; and

• 105,044,902 common shares to be issued in connection with the closing of the proposed transaction with Beckley Psytech.

Unless otherwise indicated, all information in this prospectus supplement assumes no exercise of the outstanding options or pre-funded warrants or conversion of convertible notes described above after June 30, 2025, and no exercise by the underwriters of their option to purchase up to 3,558,750 additional common shares.

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In addition, the number of common shares outstanding immediately after this offering does not include common shares that we may offer and sell in the future pursuant to our Open Market Sale Agreement^SM with Jefferies LLC, as sales agent (the “Sales Agreement”). After the expiration or waiver of the lock-up period applicable to us and described under the section of this prospectus supplement entitled “Underwriting,” we may offer and sell common shares from time to time in “at-the-market” offerings pursuant to the Sales Agreement.

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RISK FACTORS

Investment in any securities offered pursuant to this prospectus supplement and the accompanying prospectus involves risks. You should carefully consider the risk factors described below and incorporated by reference to our Annual Report on Form 10-K and our quarterly reports on Form 10-Q and all other information contained or incorporated by reference in this prospectus supplement. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities.

Risks Relating to this Offering

If you purchase our common shares sold in this offering, you will experience immediate and substantial dilution in the net tangible book value of your common shares. In addition, we may issue additional equity or convertible debt securities in the future, which may result in additional dilution to you.

The price per share of our common shares being offered may be higher than the net tangible book value per share of our outstanding common shares prior to this offering. Based on the offering price of $5.48 per share, new investors in this offering will incur immediate dilution of $4.41 per share. For a more detailed discussion of the foregoing, see the section entitled “Dilution” below. To the extent outstanding share options or warrants are exercised, there will be further dilution to new investors. In addition, we expect to issue approximately 105 million common shares in connection with the consummation of the proposed transaction with Beckley Psytech. In addition, to the extent we need to raise additional capital in the future and we issue additional common shares or securities convertible or exchangeable for our common shares, our then existing shareholders may experience dilution and the new securities may have rights senior to those of our common shares offered in this offering.

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds from this offering, including for any of the purposes described in the section entitled “Use of Proceeds,” and you will not have the opportunity as part of your investment decision to assess whether the net proceeds are being used appropriately. Because of the number and variability of factors that will determine our use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. Our management might not apply our net proceeds in ways that ultimately increase the value of your investment. We intend to use the net proceeds of this offering, together with our existing cash, cash equivalents and short-term investments, to advance the clinical development of our product candidates and programs, as well as for working capital and general corporate purposes. See the section entitled “Use of Proceeds” on page S-15 of this prospectus supplement. The failure by our management to apply these funds effectively could harm our business. We may invest our cash and cash equivalents in a manner that does not produce income or that loses value. If we do not invest or apply the net proceeds from this offering in ways that enhance shareholder value, we may fail to achieve expected financial results, which could cause our share price to decline.

The market price of our common shares may be adversely affected by market conditions affecting the stock markets in general, including price and trading fluctuations on The Nasdaq Global Market.

Market conditions may result in volatility in the level of, and fluctuations in, market prices of stocks generally and, in turn, our common shares and sales of substantial amounts of our common shares in the market, in each case being unrelated or disproportionate to changes in our operating performance. Concerns over global stability, including as a result of the COVID-19 pandemic, the ongoing military conflict between Russia and Ukraine, conflict in the Middle East, as well as political and economic conditions in the United States and abroad, have contributed to the volatility of the markets, which may have an effect on the market price of our common shares.

Future sales, or the possibility of future sales, of a substantial number of common shares could adversely affect the price of such securities.

Future sales of a substantial number of common shares, or the perception that such sales will occur, could cause a decline in the market price of our common shares. If holders sell substantial amounts of common shares on the Nasdaq Global Market, or if the market perceives that such sales may occur, the market price of the common shares and our ability to raise capital through an issue of equity securities in the future could be adversely affected.

Interim, “top-line,” and preliminary data from clinical trials that we or Beckley Psytech announce or publish from time to time may change as more patient data become available or as additional analyses are conducted, and as the data are subject to audit and verification procedures that could result in material changes in the final data.

From time to time, we or Beckley Psytech may publicly disclose preliminary or top-line data from clinical trials, which is based on a preliminary analysis of then-available data, and the results and related findings and conclusions

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are subject to change following a more comprehensive review of the data related to the particular study or trial. We and Beckley Psytech also make assumptions, estimations, calculations and conclusions as part of our respective analyses of data, and we and Beckley Psytech may not have received or had the opportunity to fully and carefully evaluate all data. As a result, the top-line or preliminary results that we or Beckley Psytech report may differ from future results of the same studies, or different conclusions or considerations may qualify such results, once additional data have been received and fully evaluated. Top-line and preliminary data also remain subject to audit and verification procedures that may result in the final data being materially different from the top-line or preliminary data we or Beckley Psytech previously published. As a result, top-line and preliminary data should be viewed with caution until the final data are available.

From time to time, we or Beckley Psytech may also disclose interim data from clinical trials. Interim data from these trials that we or Beckley Psytech may complete are subject to the risk that one or more of the clinical outcomes may materially change as subject enrollment continues and more data become available. Adverse differences between interim data and top-line, preliminary, or final data could significantly harm our respective business prospects. Further, disclosure of interim data by us or Beckley Psytech or by our respective competitors could result in volatility in the price of our common shares.

Further, others, including regulatory agencies, may not accept or agree with our respective assumptions, estimates, calculations, conclusions or analyses or may interpret or weigh the importance of data differently, which could impact the value of the particular program, the approvability or commercialization of the particular product candidate or product and our company or Beckley Psytech in general. In addition, the information we or Beckley Psytech choose to publicly disclose regarding a particular clinical trial is based on what is typically extensive information, and you or others may not agree with what we or Beckley Psytech determine is material or otherwise appropriate information to include in our respective disclosures. If the interim, top-line, or preliminary data that we or Beckley Psytech report differ from actual results, or if others, including regulatory authorities, disagree with the conclusions reached, our respective abilities to obtain approval for, and commercialize, our respective product candidates may be harmed, which could harm our respective businesses, operating results, prospects or financial conditions.

Failure to complete the proposed strategic combination with Beckley Psytech could negatively impact our share price.

If the proposed strategic combination with Beckley Psytech is not completed for any reason, we would be subject to a number of risks, including the following: we may experience negative reactions from the financial markets, including negative impacts on our valuation; we will still be required to pay certain significant expenses relating to the strategic combination; we may be required to make a termination payment as required by the SPA (including the Break Fee Shares, as defined therein); matters relating to the strategic combination (including integration planning) require substantial commitments of time and resources by our management, which may have resulted in the distraction of our management from ongoing business operations and pursuing other opportunities that could have been beneficial to us; and litigation related to any failure to complete the strategic combination or related to any enforcement proceeding may be commenced against us to perform our obligations pursuant to the SPA. If the strategic combination is not completed, the risks described in the preceding sentence may materialize and cause our share price to be negatively impacted.

The expected benefits of the Redomiciliation may not be realized, and the Redomiciliation may not be implemented or may not be implemented in a timely manner.

There can be no assurance that any or all of the anticipated benefits of the Redomiciliation will be achieved. Achieving the anticipated benefits of the Redomiciliation is subject to a number of risks and uncertainties, including factors that we do not and cannot control. In addition, if the expected benefits of the Redomiciliation do not meet expectations of investors or securities analysts, the price of our common shares following completion of the Redomiciliation may decline. Completion of the Redomiciliation is contingent on factors and circumstances of which some are not, or not completely, within our control. As a result, the Redomiciliation may not be implemented or may not be implemented according to the timeline as currently foreseen by us.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein and any free writing prospectus that we have authorized for use in connection with this offering contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. We intend such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act and Section 21E of the Exchange Act. All statements other than statements of historical facts contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein and any free writing prospectus are forward-looking statements, including without limitation statements regarding our future operating results and financial position; the success, cost, and timing of development of our product candidates, including the progress of preclinical studies and clinical trials and related milestones; the commercialization of our current product candidates and any other product candidates we may identify and pursue, if approved, including our ability to successfully build a specialty sales force and commercial infrastructure to market our current product candidates and any other product candidates we may identify and pursue; the timing of and our ability to obtain and maintain regulatory approvals; our business strategy and plans, including the benefits of our corporate restructuring and our pending corporate redomiciliation to the U.S.; potential acquisitions, partnerships and other strategic arrangements, including our pending transaction with Beckley Psytech; the ability to generate revenue from any current or future licensing agreements and other strategic arrangements, the sufficiency of our cash and cash equivalents and short-term securities to fund our operations; the plans and objectives of management for future operations and capital expenditures the number and price of our common shares to be sold in this offering; and our expected use of proceeds from this offering. The words “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect,” “could,” “would,” “project,” “plan,” “potentially,” “preliminary,” “likely,” and similar expressions are intended to identify forward-looking statements.

We have based these forward-looking statements largely on our current expectations and projections about future events and trends that we believe may affect our financial condition, results of operations, business strategy, short-term and long-term business operations and objectives, and financial needs. These forward-looking statements are neither promises nor guarantees, and are subject to a number of important factors that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation: we are a clinical-stage biopharmaceutical company and have incurred significant losses since our inception, and we expect to incur losses for the foreseeable future and may never be profitable; if we are unable to obtain funding when needed and on acceptable terms, we could be forced to delay, limit or discontinue our product candidate development efforts; our limited operating history may make it difficult for you to evaluate the success of our business and to assess our future viability; risks related to the proposed transaction with Beckley Psytech; we rely on third parties to assist in conducting our clinical trials and some aspects of our research and preclinical testing; we currently rely on qualified therapists working at third-party clinical trial sites to administer certain of our product candidates in our clinical trials and we expect this to continue upon approval, if any, of our current or future product candidates, and if third-party sites fail to recruit and retain a sufficient number of therapists or effectively manage their therapists, our business, financial condition and results of operations would be materially harmed; our product candidates are in preclinical or clinical development, which is a lengthy and expensive process with uncertain outcomes, and we cannot give any assurance that any of our product candidates will be successfully developed and/or receive regulatory approval, which is necessary before they can be commercialized; research and development of drugs targeting the central nervous system, or CNS, is particularly difficult, and it can be difficult to predict and understand why a drug has a positive effect on some patients but not others, which may reduce the likelihood our product candidates are ultimately approved and therefore may have a material adverse effect on our business and operating results; the production and sale of our product candidates may be considered illegal or may otherwise be restricted due to the use of controlled substances, which may also have consequences for the legality of investments from foreign jurisdictions and therefore we may not be successful in commercializing our product candidates in such jurisdictions, which will adversely affect our business, financial condition and results of operations; we face significant competition in an environment of rapid technological and scientific change, and there is a possibility that our competitors may achieve regulatory approval before we do or develop therapies that are safer, more advanced or more effective than ours, which may negatively impact our ability to successfully market or commercialize any product candidates we may develop and ultimately harm our financial condition; if we are unable to obtain and maintain sufficient intellectual property protection for our existing product candidates or any other product candidates that we may identify, or if the scope of the intellectual property protection we currently have or obtain in the future is not sufficiently broad, our competitors could develop and commercialize product candidates similar or identical to ours, and our ability to successfully commercialize our existing product candidates and any

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other product candidates that we may pursue may be impaired; third parties may claim that we are infringing, misappropriating or otherwise violating their intellectual property rights, the outcome of which would be uncertain and may prevent or delay our development and commercialization efforts; our future success depends on our ability to retain key employees, directors, consultants and advisors and to attract, retain and motivate qualified personnel; if we fail to maintain an effective system of disclosure controls and internal control over financial reporting our ability to produce timely and accurate financial statements or comply with applicable regulations could be impaired; the use of proceeds from this offering; our business is subject to economic, political, regulatory and other risks associated with international operations; a pandemic, epidemic, or outbreak of an infectious disease, such as the COVID-19 pandemic, may materially and adversely affect our business, including our preclinical studies, clinical trials, trial sites, third parties on whom we rely, our supply chain, our ability to raise capital, our ability to conduct regular business and our financial results, and other risks, uncertainties, and assumptions described under “Risk Factors” in Item 1A of Part I, “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in Item 7 of Part II and elsewhere in our Form 10-K for the year ended December 31, 2024, as further updated in “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in Item 2 of our Form 10-Q for the quarterly period ended June 30, 2025, in our subsequent filings with the SEC and in this prospectus supplement.

Any forward-looking statements made herein speak only as of the date of this prospectus supplement, and you should not rely on forward-looking statements as predictions of future events. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee that the future results, performance, or achievements reflected in the forward-looking statements will be achieved or will occur. Except as required by applicable law, we undertake no obligation to update any of these forward-looking statements for any reason after the date of this prospectus supplement or to conform these statements to actual results or revised expectations.

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USE OF PROCEEDS

We estimate the net proceeds from this offering will be approximately $121.2 million, or approximately $139.4 million if the underwriters’ option to purchase additional common shares from us is exercised in full, in each case after deducting the underwriting discounts and commissions and estimated offering expenses payable by us.

Although we have not finalized our full financial results for the three months ended September 30, 2025, we expect to report that we had approximately $114.6 million in cash, cash equivalents and short-term investments as of September 30, 2025. We intend to use the net proceeds of this offering, together with our existing cash, cash equivalents and short-term investments, to advance the clinical development of our product candidates and programs, as well as for working capital and general corporate purposes.

The amounts and timing of our actual expenditures will depend on numerous factors, including the progress of our clinical trials and other development efforts and other factors described under “Risk Factors” in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, as well as the amount of cash used in our operations. We may find it necessary or advisable to use the net proceeds for other purposes, and our management will have broad discretion in the application of the net proceeds. We may invest our cash, cash equivalents and short-term investments in a manner that does not produce income or that loses value. As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses of the net proceeds from this offering. Accordingly, we will retain broad discretion over the use of such proceeds.

Based on the planned use of proceeds described above and our current operating plan, we estimate that our cash, short-term securities and public equity holdings, as of the date of this prospectus supplement will be sufficient to fund our operating expenses into 2028. We may need additional funds to complete the Phase 3 study of BPL-003. We expect to continue to incur substantial additional expenditures in the near term to support our ongoing activities. We have based this estimate on assumptions that may prove to be incorrect, and we could use our available capital resources sooner than we currently expect.

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DIVIDEND POLICY

We have never paid or declared any cash dividends in the past, and we do not anticipate paying any cash dividends in the foreseeable future. We intend to retain all available funds and any future earnings to fund the further development and expansion of our business.

Under Dutch law, we may only pay dividends and other distributions from our reserves to the extent our shareholders’ equity (eigen vermogen) exceeds the sum of our paid-in and called-up share capital plus the reserves we must maintain under Dutch law or our articles of association and (if it concerns a distribution of profits) after adoption of our statutory annual accounts by our general meeting from which it appears that such dividend distribution is allowed. Subject to those restrictions, any future determination to pay dividends or other distributions from our reserves will be at the discretion of our board of directors and will depend upon a number of factors, including our results of operations, financial condition, future prospects, contractual restrictions, restrictions imposed by applicable law and other factors we deem relevant.

Under our articles of association as they will read upon the date of this prospectus, our board of directors may decide that all or part of the profits shown in our adopted statutory annual accounts will be added to our reserves. After reservation of any such profits, any remaining profits will be at the disposal of the general meeting at the proposal of our board of directors for distribution on our common shares, subject to applicable restrictions of Dutch law. Our board of directors is permitted, subject to certain requirements and applicable restrictions of Dutch law, to declare interim dividends without the approval of our general meeting. Dividends and other distributions shall be made payable no later than a date determined by us. Claims to dividends and other distributions not made within five years from the date that such dividends or distributions became payable will lapse and any such amounts will be considered to have been forfeited to us (verjaring).

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DILUTION

If you invest in our common shares, your interest will be diluted to the extent of the difference between the price per share you pay in this offering and the net tangible book value per share immediately after this offering. The net tangible book value of our common shares as of June 30, 2025 was $131.5 million, or $0.62 per share based upon 212,244,597 common shares outstanding. Net tangible book value per share is equal to our total tangible assets, less our total liabilities, divided by the total number of common shares outstanding as of June 30, 2025.

After giving effect to the issuance and sale of 23,725,000 common shares at the offering price of $5.48 per share, and after deducting commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of June 30, 2025 would have been $252.6 million, or $1.07 per share. This represents an immediate increase in net tangible book value of $0.45 per share to our existing shareholders and an immediate dilution in net tangible book value of $4.41 per share to new investors in this offering.

Net tangible book value per share as of June 30, 2025			$0.62
Increase in net tangible book value per share attributable to the offering			0.45
As adjusted net tangible book value per share after giving effect to the offering						1.07
Dilution per share to new investors participating in the offering						$4.41

If the underwriters exercise their option to purchase up to 3,558,750 additional common shares in full at the public offering price of $5.48 per share, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, the as-adjusted net tangible book value would be $1.13 per share, representing an immediate increase in net tangible book value of $0.51 per share to existing shareholders and an immediate dilution in as-adjusted net tangible book value of $4.35 per share to new investors purchasing our common shares in this offering.

A $1.00 increase in the public offering price of $5.48 per share would increase our as adjusted net tangible book value per share after this offering to $1.16 per share and dilution to new investors to $5.32 per share, after deducting commissions and estimated offering expenses payable by us. A $1.00 decrease in the public offering price of $5.48 per share would decrease our as adjusted net tangible book value per share after this offering to $0.98 per share and dilution to new investors to $3.50 per share, after deducting commissions and estimated offering expenses payable by us.

The number of our common shares to be outstanding after this offering is based on 212,244,597 common shares outstanding as of June 30, 2025, and excludes:

• 10,743,021 common shares issuable upon the exercise of options outstanding under our 2020 Employee, Director and Consultant Equity Incentive Plan, or the 2020 Plan, as of June 30, 2025 at a weighted-average exercise price of $4.90;

• 37,822,494 common shares issuable upon the exercise of options outstanding under our 2021 Incentive Award Plan, or the 2021 Plan, as of June 30, 2025 at a weighted-average exercise price of $2.76;

• 40,454,775 common shares reserved for future issuance under our 2021 Plan as of June 30, 2025;

• 257,419 common shares reserved for future issuance under the HSOP as of June 30, 2025;

• 10,877,216 common shares issuable upon the exercise of pre-funded warrants;

• 6,185,904 common shares issuable upon the conversion of convertible notes, and such common shares were issued on September 17, 2025 and October 7, 2025 in connection with the conversion of such convertible notes;

• 18,264,840 common shares issuable pursuant to subscription agreements, dated July 1, 2025, between us and the investors party thereto, and such common shares were issued on August 14, 2025 in connection with the closing of the sale of such common shares pursuant to the subscription agreements; and

• 105,044,902 common shares to be issued in connection with the closing of the proposed transaction with Beckley Psytech.

The foregoing table does not give effect to the exercise of any outstanding options or pre-funded warrants or conversion of convertible notes described above, or to the exercise by the underwriters of their option to purchase

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up to 3,558,750 additional common shares. We may raise additional capital in the future through the sale of equity or convertible debt securities. To the extent options are exercised or restricted stock units vest and settle, or we issue common shares in connection with raising additional capital, there may be further dilution to new investors.

In addition, the number of common shares outstanding immediately after this offering does not include common shares that we may offer and sell in the future pursuant to the Sales Agreement. After the expiration or waiver of the lock-up period applicable to us and described under the section of this prospectus supplement entitled “Underwriting,” we may offer and sell common shares from time to time in “at-the-market” offerings pursuant to the Sales Agreement.

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MATERIAL TAX CONSIDERATIONS

Material Dutch Tax Considerations

The following section summarizes the main material Dutch tax considerations of the acquiring, holding and disposal of our common shares, but it does not purport to be a description of all possible Dutch tax considerations that may be relevant to a holder or prospective holder of our common shares and does not purport to deal with the tax consequences applicable to all categories of investors as some investors may be subject to special treatment under applicable law (such as trusts or other similar arrangements). In view of its general nature, it should be treated with corresponding caution.

This section is based on the tax laws of the Netherlands, published regulations thereunder and published authoritative case law, all as in effect on the date hereof, including, for the avoidance of doubt, the tax rates, tax brackets and deemed returns applicable on the date hereof, and all of which are subject to change, possibly with retroactive effect. Any such change may invalidate the contents of this section, which will not be updated to reflect such change. Where this section refers to “the Netherlands” or “Dutch” it refers only to the part of the Kingdom of the Netherlands located in Europe.

This section is intended as general information only and is not Dutch tax advice or a complete description of all Dutch tax consequences relating to the acquisition, holding and disposal of our common shares. Holders or prospective holders of our common shares should consult their own tax advisor regarding the Dutch tax consequences relating to the acquisition, holding and disposal of our common shares in light of their particular circumstances.

This section does not describe any Dutch tax considerations or consequences arising from the Dutch Minimum Tax Act 2024 (Wet minimumbelasting 2024; the Dutch implementation of Directive (EU) 2022/2523 of 14 December 2022 on ensuring a global minimum level of taxation for multinational enterprise groups and large-scale domestic groups in the European Union) which may be relevant for a particular holder.Please note that this section does not address Dutch tax considerations for:

(i)
a holder of common shares if such holder has a substantial interest (aanmerkelijk belang) or deemed substantial interest (fictief aanmerkelijk belang) in the Company under the Dutch Income Tax Act 2001 (Wet inkomstenbelasting 2001). Generally speaking, a holder is considered to hold a substantial interest in the Company, if such holder alone or, in the case of an individual, together with such holder’s partner for Dutch income tax purposes, or any relatives by blood or marriage in the direct line (including foster children), directly or indirectly, holds (i) an interest of 5% or more of the total issued and outstanding capital of the Company or of 5% or more of the issued and outstanding capital of a certain class of shares; or (ii) rights to acquire, directly or indirectly, such interest; or (iii) certain profit-sharing rights that relate to 5% or more of the Company’s annual profits or to 5% or more of the Company’s liquidation proceeds. A deemed substantial interest may arise if a substantial interest (or part thereof) in the Company has been disposed of, or is deemed to have been disposed of, on a non-recognition basis;

(ii)
a holder of common shares who is an individual for whom the common shares or any benefit derived from the common shares are a remuneration or deemed to be a remuneration for employment activities performed by such holder or certain individuals related to such holder (as defined in the Dutch Income Tax Act 2001);

(iii)
a holder of common shares, if the common shares held by the holder qualify or qualified as a participation (deelneming) for purposes of the Dutch Corporate Income Tax Act 1969 (Wet op de vennootschapsbelasting 1969). Generally, a holder’s shareholding, or right to acquire, of 5% or more in the Company’s nominal paid-up share capital qualifies as a participation. A holder may also have a participation if such holder does not have a shareholding of 5% or more but a related entity (statutorily defined term) has a participation, or the Company is a related entity (statutorily defined term);

(iv)
a holder of common shares which is or who is entitled to the dividend withholding tax exemption (inhoudingsvrijstelling) with respect to any income (opbrengst) derived from the common shares (as defined in Article 4 of the Dutch Dividend Withholding Tax Act 1965 (Wet op de dividendbelasting)). Generally, a holder of common shares may be entitled or required to apply, subject to certain other requirements, the dividend withholding tax exemption if it is an entity and holds an interest of 5% or more in the Company’s nominal paid-up share capital;

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(v)
pension funds, investment institutions (fiscale beleggingsinstellingen) and exempt investment institutions (vrijgestelde beleggingsinstellingen) (each as defined in the Dutch Corporate Income Tax Act 1969) and other entities that are, in whole or in part, not subject to or exempt from Dutch corporate income tax, entities that have a function comparable to an investment institution or a tax-exempt investment institution, as well as entities that are exempt from income tax in their country of residence, such country of residence being another state of the European Union, Norway, Liechtenstein, Iceland or any other state with which the Netherlands has agreed to exchange information in line with international standards;

(vi)
holders of common shares that are entities resident in Aruba, Curaçao, or Sint Maarten, conducting a business through a permanent establishment (vaste inrichting) or permanent representative (vaste vertegenwoordiger) in Bonaire, Sint Eustatius, or Saba, to which the common shares are attributable; and

(vii)
holders of our outstanding options, restricted stock units, pre-funded warrants and convertible notes.

Withholding Tax on Dividends

Regular Dutch Dividend Withholding Tax

Dividends distributed by us are generally subject to Dutch dividend withholding tax at a rate of 15%. Generally, we are responsible for the withholding of such dividend withholding tax at source; the Dutch dividend withholding tax is for the account of the holder of common shares.

The expression “dividends distributed” includes, but is not limited to:

(i)
distributions in cash or in kind, deemed and constructive distributions and repayments of paid-in capital not recognized for Dutch dividend withholding tax purposes;

(ii)
liquidation proceeds, proceeds of redemption of common shares, or proceeds of the repurchase of common shares (other than as temporary portfolio investment; tijdelijke belegging) by the Company or one of the Company’s subsidiaries or other affiliated entities, in each case to the extent such proceeds exceed the average paid-in capital of those common shares as recognized for purposes of Dutch dividend withholding tax;

(iii)
an amount equal to the par value of common shares issued or an increase of the par value of common shares, to the extent that no related contribution, recognized for purposes of Dutch dividend withholding tax, has been made or will be made; and

(iv)
partial repayment of the paid-in capital, recognized for purposes of Dutch dividend withholding tax, if and to the extent that the Company has “net profits” (zuivere winst), unless (i) the Company’s general meeting of shareholders has resolved in advance to make such repayment and (ii) the par value of the common shares concerned has been reduced by an equal amount by way of an amendment of the Company’s articles of association. The term “net profits” includes anticipated profits that have yet to be realized.

Corporate legal entities that are resident or deemed to be resident of the Netherlands for Dutch corporate income tax purposes (“Dutch Resident Entities”) generally are entitled to an exemption from, or a credit for, any Dutch dividend withholding tax against their Dutch corporate income tax liability. The credit in any given year is, however, limited to the amount of Dutch corporate income tax payable in respect of the relevant year with an indefinite carry forward of any excess amount. Individuals who are resident or deemed to be resident of the Netherlands for Dutch personal income tax purposes (“Dutch Resident Individuals”) generally are entitled to a credit for any Dutch dividend withholding tax against their Dutch personal income tax liability and to a refund of any residual Dutch dividend withholding tax. The above generally also applies to holders of common shares that are neither resident nor deemed to be resident of the Netherlands (“Non-Resident Holders”) if the common shares are attributable to a Dutch permanent establishment of such Non-Resident Holder.

A holder of common shares resident of a country other than the Netherlands may, depending on such holder's specific circumstances, be entitled to exemptions from, reduction of, or full or partial refund of, Dutch dividend withholding tax under Dutch domestic tax law, EU law, or treaties for the avoidance of double taxation in effect between the Netherlands and such other country.

Dividend stripping

According to Dutch domestic anti-dividend stripping rules, no credit against Dutch tax, exemption from, reduction, or refund of Dutch dividend withholding tax will be granted if the recipient of the dividends the Company

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paid is not considered the beneficial owner (uiteindelijk gerechtigde; as described in the Dutch Dividend Withholding Tax Act 1965) of those dividends. This legislation generally targets situations in which a shareholder retains its economic interest in shares but reduces the withholding tax costs on dividends by a transaction with another party. It is not required for these rules to apply that the recipient of the dividends is aware that a dividend stripping transaction took place. The Dutch State Secretary of Finance takes the position that the definition of beneficial ownership introduced by this legislation will also be applied in the context of a double taxation convention. The burden of proof with respect to beneficial ownership of dividends distributed by the Company rests on the Dutch tax authorities. If, however, a shareholder would receive dividends, including dividends on our common shares, in a calendar year in respect of which an aggregate amount of EUR 1,000 in Dutch dividend withholding tax would otherwise be due based on the rate of 15%, the burden of proof with respect to beneficial ownership of such dividends lies with the shareholder. Furthermore, for shares traded on a regulated market, including our common shares, it has been codified that the record date is used when determining the person who is entitled to the dividend.

Conditional Withholding Tax on Dividends

In addition to the regular Dutch dividend withholding tax as described above, a Dutch conditional withholding tax will be imposed on dividends distributed by the Company to a Related Entity (as defined below), if such Related Entity:

(i)
is considered to be resident (gevestigd) in a jurisdiction that is listed in the yearly updated Dutch Regulation on low-taxing states and non-cooperative jurisdictions for tax purposes (Regeling laagbelastende staten en niet-coöperatieve rechtsgebieden voor belastingdoeleinden) (a “Listed Jurisdiction”); or

(ii)
has a permanent establishment located in a Listed Jurisdiction to which the common shares are attributable; or

(iii)
holds the common shares with the main purpose or one of the main purposes of avoiding taxation for another person or entity and there is an artificial arrangement or transaction or a series of artificial arrangements or transactions; or

(iv)
is not considered to be the beneficial owner of the common shares in its jurisdiction of residence because such jurisdiction treats another entity as the beneficial owner of the common shares (a hybrid mismatch); or

(v)
is not resident in any jurisdiction (also a hybrid mismatch); or

(vi)
is a reverse hybrid (within the meaning of Article 2(11) of the Dutch Corporate Income Tax Act 1969), if and to the extent (x) there is a participant in the reverse hybrid holding a Qualifying Interest in the reverse hybrid, (y) the jurisdiction of residence of such participant treats the reverse hybrid as transparent for tax purposes and (z) such participant would have been subject to the Dutch conditional withholding tax in respect of dividends distributed by the Company without the interposition of the reverse hybrid, all within the meaning of the Dutch Withholding Tax Act 2021 (Wet bronbelasting 2021).

For purposes of this section:

• “Related Entity” means an entity (i) that has a Qualifying Interest in the Company or (ii) in which a third party has a Qualifying Interest if such third party also has a Qualifying Interest in the Company.

• “Qualifying Interest” means a direct or indirectly held interest – either by an entity individually or, if an entity is part of a Qualifying Unity, jointly – that enables such entity or such Qualifying Unity to exercise a definitive influence over another entity’s decisions and allows it to determine that other entity’s activities (as interpreted by the European Court of Justice in case law on the right of freedom of establishment (vrijheid van vestiging)).

• “Qualifying Unity” means entities acting together with the main purpose or one of the main purposes of avoiding Dutch conditional withholding tax at the level of any of those entities (kwalificerende eenheid).

The Dutch conditional withholding tax on dividends will be imposed at the highest Dutch corporate income tax rate in effect at the time of the distribution (2025: 25.8%). The Dutch conditional withholding tax on dividends will be reduced, but not below zero, by any regular Dutch dividend withholding tax withheld in respect of the same

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dividend distribution. As such, based on the currently applicable rates, the overall effective tax rate of withholding the regular Dutch dividend withholding tax (as described above) and the Dutch conditional withholding tax on dividends will not exceed the highest corporate income tax rate in effect at the time of the distribution (2025: 25.8%).

Taxes on income and capital gains

Dutch Resident Entities

Generally, if the holder of common shares is a Dutch Resident Entity, any income derived or deemed to be derived from the common shares or any capital gain realized on the disposal or deemed disposal of the common shares is subject to Dutch corporate income tax at a rate of 19% with respect to taxable profits up to €200,000 and 25.8% with respect to taxable profits in excess of that amount (rates and brackets for 2025).

Dutch Resident Individuals

If the holder of common shares is a Dutch Resident Individual, any income derived or deemed to be derived from the common shares or any capital gains realized on the disposal or deemed disposal of the common shares is subject to Dutch personal income tax at the progressive rates (with a maximum of 49.50% for 2025), if:

(i)
the common shares are attributable to an enterprise from which the holder of common shares derives a share of the profit, whether as an entrepreneur (ondernemer) or as a person who has a co-entitlement to the net worth (medegerechtigd tot het vermogen) of such enterprise without being a shareholder (as defined in the Dutch Income Tax Act 2001); or

(ii)
the holder of common shares is considered to perform activities with respect to the common shares that go beyond ordinary asset management (normaal, actief vermogensbeheer) or otherwise derives benefits from the common shares that are taxable as benefits from miscellaneous activities (resultaat uit overige werkzaamheden).

Taxation of savings and investments

If the above-mentioned conditions (i) and (ii) do not apply to the Dutch Resident Individual, the common shares will be subject to an annual Dutch income tax under the regime for savings and investments (inkomen uit sparen en beleggen). Taxation only occurs insofar the Dutch Resident Individual’s net investment assets for the year exceed a statutory threshold (heffingvrij vermogen). The net investment assets for the year are the fair market value of the investment assets less the fair market value of the liabilities on January 1 of the relevant calendar year (reference date; peildatum). Actual income or capital gains realized in respect of the common shares are in principle not subject to Dutch income tax.

The Dutch Resident Individual’s assets and liabilities taxed under this regime, including the common shares, are allocated over the following three categories: (a) bank savings (banktegoeden), (b) other investments (overige bezittingen), including the common shares, and (c) liabilities (schulden). The taxable benefit for the year (voordeel uit sparen en beleggen) is equal to the product of (x) the total deemed return divided by the sum of bank savings, other investments and liabilities and (y) the sum of bank savings, other investments and liabilities minus the statutory threshold, and is taxed at a flat rate of 36% (rate for 2025).The deemed return applicable to other investments, including the common shares, is set at 5.88% for the calendar year 2025. Transactions in the three-month period before and after January 1 of the relevant calendar year implemented to arbitrate between the deemed return percentages applicable to bank savings, other investments and liabilities will for this purpose be ignored if the holder of common shares cannot sufficiently demonstrate that such transactions are implemented for other than tax reasons.

On June 6 and 14, 2024, the Dutch Supreme Court (Hoge Raad) ruled that the Dutch income tax regime for savings and investments as described above (the “Box 3 Regime”) in certain specific circumstances contravenes with Section 1 of the First Protocol to the European Convention on Human Rights in combination with Section 14 of the European Convention on Human Rights (the “Rulings”). In the Rulings, the Dutch Supreme Court introduced a rebuttal provision (tegenbewijsregeling) pursuant to which taxpayers have the possibility to demonstrate that the actual return realized by the taxpayer in respect of their investments assets (as calculated in line with the rules as set out in the Rulings), is less than the deemed return realized by the taxpayer in respect of those assets (as calculated in accordance with the rules of the Box 3 Regime). The rebuttal provision introduced by the Dutch Supreme Court as well as the rules set out in the Rulings have been implemented in Dutch tax law pursuant to the Dutch Box 3 Rebuttal Scheme Act (Wet tegenbewijsregeling box 3). If the taxpayer successfully demonstrates that the actual

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return is less than the deemed return (using a standardized form), the taxpayer will be taxed on the actual return instead of the deemed return. The Dutch Box 3 Rebuttal Scheme Act offers a temporary solution until a new Box 3 regime is introduced, which is expected as of 1 January 2028 at the earliest.

Holders of common shares are advised to consult their own tax advisor to ensure that the tax in respect of the common shares is levied in accordance with the applicable Dutch tax rules at the relevant time.

Non-residents of the Netherlands

A holder of common shares that is neither a Dutch Resident Entity nor a Dutch Resident Individual will not be subject to Dutch tax in respect of income derived or deemed to be derived from the common shares or in respect of any capital gains realized on the disposal or deemed disposal of the common shares, provided that:

(i)
such holder does not have an interest in an enterprise or deemed enterprise (as defined in the Dutch Income Tax Act 2001 and the Dutch Corporate Income Tax Act 1969, as applicable) which, in whole or in part, is either effectively managed in the Netherlands or carried on through a permanent establishment, a deemed permanent establishment or a permanent representative in the Netherlands and to which enterprise or part of an enterprise the common shares are attributable; and

(ii)
in the event the holder is an individual, such holder does not carry out any activities in the Netherlands with respect to the common shares that go beyond ordinary asset management and does not otherwise derive benefits from the common shares that are taxable as benefits from miscellaneous activities in the Netherlands.

Gift and inheritance taxes

Dutch Resident Individuals

Gift or inheritance taxes will arise in the Netherlands with respect to a transfer of common shares by way of a gift by, or on the death of, a holder of common shares who is resident or deemed resident of the Netherlands at the time of the gift or such holder’s death.

Non-residents of the Netherlands

No gift or inheritance taxes will arise in the Netherlands with respect to the transfer of common shares by way of a gift by, or on the death of, a holder of common shares that is neither a resident nor deemed to be a resident of the Netherlands, unless:

(i)
in the case of a gift of the common shares by an individual who at the date of the gift was neither a resident nor deemed to be a resident of the Netherlands, such individual dies within 180 days after the date of the gift, while being a resident or deemed to be a resident of the Netherlands; or

(ii)
in the case of a gift of a common share is made under a condition precedent, the holder or common shares is resident or is deemed to be resident of the Netherlands at the time the condition is fulfilled; or

(iii)
the transfer is otherwise construed as a gift or inheritance made by, or on behalf of, a person who, at the time of the gift or death, is or is deemed to be resident of the Netherlands.

For purposes of Dutch gift and inheritance taxes, amongst others, a person that holds the Dutch nationality will be deemed to be resident of the Netherlands if such person has been a resident of the Netherlands at any time during the ten years preceding the date of the gift or such person’s death.

Additionally, for purposes of Dutch gift tax, amongst others, a person not holding the Dutch nationality will be deemed to be resident of the Netherlands if such person has been resident in the Netherlands at any time during the twelve months preceding the date of the gift. Applicable tax treaties may override deemed residency.

Value Added Tax

In general, no Dutch Value Added Tax is payable by a holder of common shares in respect of payments in consideration for the holding or disposal of common shares.

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Stamp Duties

No Dutch documentation taxes (commonly referred to as stamp duties) will be payable by a holder of common shares in respect of any payment in consideration for the holding or disposal or exercise, as applicable, of the common shares.

Material United States Federal Income Tax Considerations

The following discussion describes certain U.S. federal income tax consequences to U.S. Holders (as defined below) of an investment in the common shares. This summary applies only to U.S. Holders that acquire our common shares pursuant to this offering in exchange for cash, hold such common shares as capital assets within the meaning of Section 1221 of the Code and have the U.S. dollar as their functional currency.

This discussion is based on the tax laws of the United States as in effect on the date of this prospectus supplement, including the Code and U.S. Treasury regulations in effect or, in some cases, proposed, as of the date of this prospectus supplement, as well as judicial and administrative interpretations thereof available on or before such date. All of the foregoing authorities are subject to change, and any such change could apply retroactively and could affect the U.S. federal income tax consequences described below. The statements in this prospectus supplement are not binding on the U.S. Internal Revenue Service, or the IRS, or any court, and thus we can provide no assurance that the U.S. federal income tax consequences discussed below will not be challenged by the IRS or will be sustained by a court if challenged by the IRS. Furthermore, this summary does not address any estate or gift tax consequences, any state, local or non-U.S. tax consequences or any other tax consequences other than U.S. federal income tax consequences.

The following discussion does not describe all the tax consequences that may be relevant to any particular investor or to persons in special tax situations such as:

• banks and certain other financial institutions;

• regulated investment companies;

• real estate investment trusts;

• insurance companies;

• broker-dealers;

• traders that elect to mark the common shares to market;

• tax-exempt entities;

• persons liable for alternative minimum tax or the Medicare contribution tax on net investment income;

• U.S. expatriates;

• persons holding common shares as part of a straddle, hedging, constructive sale, conversion or integrated transaction;

• persons that actually or constructively own 10% or more of our shares by vote or value;

• persons subject to special tax accounting rules who are required to take any item of gross income with respect to the common shares into account no later than when it is taken into account in an applicable financial statement;

• persons that are resident or ordinarily resident in or have a permanent establishment in a jurisdiction outside the United States;

• persons who acquired common shares pursuant to the exercise of any employee share option or otherwise as compensation; or

• persons holding common shares through partnerships or other pass-through entities or arrangements.

PROSPECTIVE PURCHASERS ARE URGED TO CONSULT THEIR TAX ADVISORS ABOUT THE APPLICATION OF THE U.S. FEDERAL TAX RULES TO THEIR PARTICULAR CIRCUMSTANCES AS WELL AS THE STATE, LOCAL AND NON-U.S. TAX CONSEQUENCES TO THEM OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF COMMON SHARES.

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As used herein, the term “U.S. Holder” means a beneficial owner of common shares that, for U.S. federal income tax purposes, is or is treated as:

• an individual who is a citizen or resident of the United States;

• a corporation created or organized in or under the laws of the United States, any state thereof or the District of Columbia;

• an estate whose income is subject to U.S. federal income taxation regardless of its source; or

• a trust that (1) is subject to the supervision of a court within the United States and the control of one or more U.S. persons or (2) has a valid election in effect under applicable U.S. Treasury regulations to be treated as a U.S. person.

The tax treatment of a partner in an entity or arrangement treated as a partnership for U.S. federal income tax purposes that holds common shares generally will depend on such partner’s status and the activities of the partnership. A U.S. Holder that is a partner in such partnership should consult its tax advisor.

Passive Foreign Investment Company Considerations

A non-U.S. corporation will be classified as a PFIC for any taxable year if either: (a) at least 75% of its gross income is “passive income” for purposes of the PFIC rules or (b) at least 50% of the value of its assets (determined on the basis of a quarterly average) is attributable to assets that produce or are held for the production of passive income. The PFIC rules also contain a look-through rule whereby a non-U.S. corporation will be treated as owning its proportionate share of the gross assets and earning its proportionate share of the gross income of any other corporation in which it owns, directly or indirectly, 25% or more (by value) of the stock. Based on our historic and anticipated operations and composition of assets, we believe we were not a PFIC for our taxable year ended on December 31, 2024, and we do not expect to become a PFIC for the foreseeable future. However, because this determination is made on an annual basis after the close of each taxable year and is factual in nature, no assurance can be given as to whether we would be a PFIC for any taxable year.

If under the PFIC rules, if we were considered a PFIC at any time that a U.S. Holder holds its common shares, we would continue to be treated as a PFIC with respect to such holder’s investment unless (i) we have ceased to be a PFIC and (ii) the U.S. Holder has made a “deemed sale” election under the PFIC rules. If such election is made, the U.S. Holder will be deemed to have sold its common shares at their fair market value on the last day of the last taxable year in which we were a PFIC, and any gain from the deemed sale would be subject to the rules described in the following paragraph. After the deemed sale election, so long as we do not become a PFIC in a subsequent taxable year, the common shares with respect to which such election was made will not be treated as shares in a PFIC. U.S. Holders should consult their tax advisors as to the possibility and consequences of making a deemed sale election if we are (or were to become) and then cease to be a PFIC, and such election becomes available.

In the absence of a deemed sale election described above, if we are considered a PFIC at any time that a U.S. Holder holds its common shares, unless the U.S. Holder makes one of the elections described below, any gain recognized by the U.S. Holder on a sale or other disposition of the common shares, as well as the amount of any “excess distribution” (defined below) received by such holder, would be allocated ratably over the U.S. Holder’s holding period for the common shares. The amounts allocated to the taxable year of the sale or other disposition (or the taxable year of receipt, in the case of an excess distribution) and to any year before we became a PFIC would be taxed as ordinary income. The amount allocated to each other taxable year would be subject to tax at the highest rate in effect for individuals or corporations, as appropriate, for that taxable year, and an interest charge would be imposed. For purposes of these rules, an excess distribution is the amount by which any distribution received by a U.S. Holder on its common shares in a taxable year exceeds 125% of the average of the annual distributions on the common shares received during the preceding three years or the U.S. Holder’s holding period, whichever is shorter.

If we are treated as a PFIC with respect to a U.S. Holder for any taxable year, the U.S. Holder will be deemed to own its pro rata share of common shares in any of our subsidiaries that are also PFICs, and the U.S. Holder may be subject to the tax consequences described above with respect to the shares of such lower-tier PFIC such U.S. Holder would be deemed to own.

If we are a PFIC for any taxable year during which a U.S. Holder holds common shares, in lieu of being subject to the tax and interest charge rules discussed above, a U.S. Holder may make an election to include gain on the stock of a PFIC as ordinary income under a mark-to-market method, provided that such common shares are “marketable.”

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Common shares will be marketable if they are “regularly traded” on certain U.S. stock exchanges or on a foreign stock exchange that meets certain conditions. For these purposes, the common shares generally will be considered regularly traded during a calendar year if they are traded, other than in de minimis quantities, on at least 15 days during each quarter. Any trades that have as their principal purpose meeting this requirement will be disregarded. However, because a mark-to-market election cannot be made for any lower-tier PFICs that we may own, a U.S. Holder will generally continue to be subject to the PFIC rules discussed above with respect to such holder’s indirect interest in any investments we hold that are treated as an equity interest in a PFIC for United States federal income tax purposes. As a result, it is possible that any mark-to-market election will be of limited benefit.

If a U.S. Holder makes an effective mark-to-market election, in each year that we are a PFIC, such U.S. Holder will include in ordinary income the excess of the fair market value of such U.S. Holder’s common shares at the end of the year over such U.S. Holder’s adjusted tax basis in the common shares. Such U.S. Holder will be entitled to deduct as an ordinary loss in each such year the excess of such U.S. Holder’s adjusted tax basis in the common shares over their fair market value at the end of the year, but only to the extent of the net amount previously included in income as a result of the mark-to-market election. If a U.S. Holder makes an effective mark-to-market election, in each year that we are a PFIC, any gain such U.S. Holder recognizes upon the sale or other disposition of such U.S.  Holder’s common shares will be treated as ordinary income and any loss will be treated as ordinary loss, but only to the extent of the net amount of previously included income as a result of the mark-to-market election.

A U.S. Holder’s adjusted tax basis in the common shares will be increased by the amount of any income inclusion and decreased by the amount of any deductions under the mark-to-market rules discussed above. If a U.S. Holder makes an effective mark-to-market election, it will be effective for the taxable year for which the election is made and all subsequent taxable years unless the common shares are no longer regularly traded on a qualified exchange or the IRS consents to the revocation of the election. U.S. Holders should consult their tax advisers about the availability of the mark-to-market election, and whether making the election would be advisable in their particular circumstances.

In certain circumstances, a U.S. equity holder in a PFIC may avoid the adverse tax and interest charge regime described above by timely making a “qualified electing fund,” or QEF, election. If a U.S. Holder makes a QEF election with respect to the common shares, the U.S. Holder generally will include in gross income its pro rata share of our ordinary earnings (as ordinary income) and net capital gain (as long-term capital gain), in each case whether or not actually distributed, on a current basis, and the U.S. Holder’s adjusted basis in the common shares will be increased by the amounts so included in gross income. Any subsequent distribution by us that is paid out of the earnings and profits that were previously so included in gross income of the U.S. Holder generally will not be taxable as a dividend to the U.S. Holder, and the U.S. Holder’s adjusted basis in the common shares will decrease by the amount of the distribution not treated as a taxable dividend. If a U.S. Holder has timely made a QEF election with respect to the common shares, any gain such U.S. Holder recognizes upon the sale or other disposition of the common shares generally will be treated as capital gain, and no interest charge will be imposed.

However, a U.S. Holder may make a QEF election with respect to the common shares only if we agree to furnish the holder annually with a PFIC annual information statement as specified in the applicable U.S. Treasury regulations. If we determine we are a PFIC for any taxable year, we will use reasonable efforts to provide to the U.S. Holders such information as the IRS may require, including a PFIC annual information statement, in order to enable the U.S. Holders to make and maintain a QEF election. However, there can be no assurance that we will be able to timely provide such required information to the U.S. Holders.

If a U.S. Holder owns common shares during any year in which we are treated as a PFIC with respect to such U.S. Holder and the U.S. Holder recognizes gain on a disposition of such common shares or receives distributions with respect to such common shares, the U.S. Holder generally will be required to file an IRS Form 8621 with respect to us, generally with the U.S. Holder’s federal income tax return for that year. If we are a PFIC for a given taxable year, you should consult your tax advisor concerning your annual filing requirements.

U.S. Holders should consult their tax advisors about the potential application of the PFIC rules to an investment in the common shares.

Taxation of Distributions

Subject to the PFIC considerations discussed above under “—Passive Foreign Investment Company Considerations,” the gross amount of distributions made by us with respect to common shares (including the amount of any non-U.S. taxes withheld therefrom) generally will constitute ordinary dividend income in the year received,

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to the extent such distributions are paid out of the our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Because we do not maintain calculations of its earnings and profits under U.S. federal income tax principles, a U.S. Holder should expect all cash distributions will be reported as dividends for U.S. federal income tax purposes. Such dividends will not be eligible for the dividends-received deduction allowed to U.S. corporations with respect to dividends received from other U.S. corporations. Since we may be treated as a PFIC, dividends received by non-corporate U.S. Holders may not be treated as “qualified dividend income,” which is taxed at the lower applicable capital gains rate.

The amount of any distribution paid in foreign currency will be equal to the U.S. dollar value of such currency, translated at the spot rate of exchange on the date such distribution is received, regardless of whether the payment is in fact converted into U.S. dollars at that time. If the dividend is converted into U.S. dollars on the date of receipt, a U.S. Holder should not be required to recognize foreign currency gain or loss in respect of the dividend income. A U.S. Holder may have foreign currency gain or loss if the dividend is converted into U.S. dollars after the date of receipt. In general, foreign currency gain or loss will be treated as U.S.-source ordinary income or loss.

Dividends on the common shares generally will constitute foreign source income for foreign tax credit limitation purposes. Subject to certain complex conditions and limitations, Dutch taxes withheld on any distributions on the common shares may be eligible for credit against a U.S. Holder’s federal income tax liability or, at such holder’s election, may be eligible for as a deduction in computing such holder’s U.S. federal taxable income. Certain U.S. Treasury regulations may restrict the availability of any foreign tax credit based on, among other things, the nature of the withholding tax imposed by the foreign jurisdiction. However, pursuant to guidance from the IRS which indicates that the U.S. Department of the Treasury and the IRS are considering proposing amendments to such U.S. Treasury Regulations, taxpayers may, subject to certain conditions, defer the application of many aspects of such U.S. Treasury regulations for taxable years beginning on or after December 28, 2021 and ending before the date that a notice or other guidance withdrawing or modifying the temporary relief is issued (or any later date specified in such notice or other guidance). U.S. Holders are urged to consult their tax advisors regarding the creditability of any such tax imposed by the Netherlands. If a refund of the tax withheld is available under the laws of the Netherlands or under the tax treaty between the United States and the Netherlands, the amount of tax withheld that is refundable will not be eligible for such credit against a U.S. Holder’s U.S. federal income tax liability (and will not be eligible for the deduction against U.S. federal taxable income). The limitation on foreign taxes eligible for credit is calculated separately with respect to specific classes of income. For this purpose, dividends distributed by us with respect to common shares will generally constitute “passive category income.” The rules relating to the determination of the U.S. foreign tax credit are complex, and U.S. Holders should consult their tax advisors regarding the availability of a foreign tax credit in their particular circumstances and the possibility of claiming an itemized deduction (in lieu of the foreign tax credit) for any foreign taxes paid or withheld.

Sale or Other Taxable Disposition of Common Shares

Subject to the PFIC considerations discussed above under “—Passive Foreign Investment Company Considerations,” upon a sale or other taxable disposition of common shares, a U.S. Holder will recognize gain or loss in an amount equal to the difference between the amount realized and the U.S. Holder’s adjusted tax basis in such common shares. Any such gain or loss generally would be treated as long-term capital gain or loss if the U.S. Holder’s holding period in the common shares exceeds one year; however, as discussed above, so long as we are a PFIC, such gain or loss would be subject to the special rules discussed above. Gain or loss, if any, realized by a U.S. Holder on the sale or other disposition of common shares generally will be treated as U.S. source gain or loss for U.S. foreign tax credit limitation purposes.

If the consideration received upon the sale or other disposition of common shares is paid in foreign currency, the amount realized will be the U.S. dollar value of the payment received, translated at the spot rate of exchange on the date of taxable disposition. The common shares will be listed and traded on Nasdaq. If the common shares are treated as traded on an established securities market for U.S. federal income tax purposes and the relevant U.S. Holder is either a cash basis taxpayer or an accrual basis taxpayer who has made a special election (which must be applied consistently from year to year and cannot be changed without the consent of the IRS), such holder will determine the U.S. dollar value of the amount realized in foreign currency by translating the amount received at the spot rate of exchange on the settlement date of the sale. An accrual basis taxpayer that does not make the special election will recognize exchange gain or loss to the extent attributable to the difference between the exchange rates on the sale date and the settlement date, and such exchange gain or loss generally will constitute U.S.-source ordinary income or loss.

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A U.S. Holder’s initial tax basis in common shares generally will equal the cost of such common shares. If a U.S. Holder used foreign currency to purchase the common shares, the cost of the common shares generally will be the U.S. dollar value of the foreign currency purchase price on the date of purchase, translated at the spot rate of exchange on that date. If the common shares are treated as traded on an established securities market for U.S. federal income tax purposes and the relevant U.S. Holder is either a cash basis taxpayer or an accrual basis taxpayer who has made the special election described above, the U.S. Holder will determine the U.S. dollar value of the cost of such common shares by translating the amount paid at the spot rate of exchange on the settlement date of the purchase.

Information Reporting and Backup Withholding

Dividend payments with respect to common shares and proceeds from the sale, exchange or redemption of common shares may be subject to information reporting to the IRS and U.S. backup withholding. A U.S. Holder may be eligible for an exemption from backup withholding if the U.S. Holder furnishes a correct taxpayer identification number and makes any other required certification or is otherwise exempt from backup withholding. U.S. Holders who are required to establish their exempt status may be required to provide such certification on IRS Form W-9. U.S. Holders should consult their tax advisors regarding the application of the U.S. information reporting and backup withholding rules.

Backup withholding is not an additional tax. Amounts withheld as backup withholding may be credited against a U.S. Holder’s U.S. federal income tax liability, and such U.S. Holder may obtain a refund of any excess amounts withheld under the backup withholding rules by timely filing an appropriate claim for refund with the IRS and furnishing any required information.

Additional Information Reporting Requirements

Certain U.S. Holders who are individuals (and certain entities) that hold an interest in “specified foreign financial assets” (which may include the common shares) in excess of applicable thresholds are required to report information relating to such assets, subject to certain exceptions (including an exception for common shares held in accounts maintained by certain financial institutions). “Specified foreign financial assets” include any financial accounts held at a non-U.S. financial institution, as well as securities issued by a non-U.S. issuer (such as the common shares) that are not held in accounts maintained by financial institutions. Penalties can apply if U.S. Holders fail to satisfy such reporting requirements. U.S. Holders should consult their tax advisors regarding the applicability of these requirements to their acquisition and ownership of common shares.

THE DISCUSSION ABOVE IS A GENERAL SUMMARY. IT DOES NOT COVER ALL TAX MATTERS THAT MAY BE IMPORTANT TO YOU. EACH PROSPECTIVE PURCHASER SHOULD CONSULT ITS OWN TAX ADVISOR ABOUT THE TAX CONSEQUENCES OF AN INVESTMENT IN COMMON SHARES UNDER THE INVESTOR’S OWN CIRCUMSTANCES.

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UNDERWRITING

Subject to the terms and conditions set forth in the underwriting agreement, dated October 16, 2025, among us, Jefferies LLC, as the representative of the underwriters named below of this offering, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the respective number of common shares shown opposite its name below:

Underwriter			Number of Common Shares
Jefferies LLC			16,607,500
Berenberg Capital Markets LLC			3,558,750
Oppenheimer & Co. Inc.			2,372,500
Canaccord Genuity LLC			1,186,250
Total			23,725,000

The underwriting agreement provides that the obligations of the several underwriters are subject to certain conditions precedent such as the receipt by the underwriters of officers’ certificates and legal opinions and approval of certain legal matters by their counsel. The underwriting agreement provides that the underwriters will purchase all of the common shares if any of them are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaulting underwriters may be increased or the underwriting agreement may be terminated. We have agreed to indemnify the underwriters and certain of their controlling persons against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters have advised us that, following the completion of this offering, they currently intend to make a market in the common shares as permitted by applicable laws and regulations. However, the underwriters are not obligated to do so, and the underwriters may discontinue any market-making activities at any time without notice in their sole discretion. Accordingly, no assurance can be given as to the liquidity of the trading market for the common shares, that you will be able to sell any of the common shares held by you at a particular time or that the prices that you receive when you sell will be favorable. 

The underwriters are offering the common shares subject to their acceptance of the common shares from us and subject to prior sale. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part. In addition, the underwriters have advised us that they do not intend to confirm sales to any account over which they exercise discretionary authority.

Commission and Expenses

The underwriters have advised us that they propose to offer the common shares to the public at the initial public offering price set forth on the cover page of this prospectus and to certain dealers, which may include the underwriters, at that price less a concession not in excess of $0.209926 per common share. After the offering, the initial public offering price, concession and reallowance to dealers may be reduced by the representatives. No such reduction will change the amount of proceeds to be received by us as set forth on the cover page of this prospectus supplement.

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The following table shows the public offering price, the underwriting discounts and commissions that we are to pay the underwriters and the proceeds, before expenses, to us in connection with this offering. Such amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase additional common shares.

			Per Share						Total
			Without Option to Purchase Additional Common Shares			With Option to Purchase Additional Common Shares			Without Option to Purchase Additional Common Shares			With Option to Purchase Additional Common Shares
Public offering price			$5.48			$5.48			$130,013,000.00			$149,514,950.00
Underwriting discounts and commissions paid by us			$0.349876			$0.349876			$8,300,808.10			$9,545,929.32
Proceeds to us, before expenses			$5.130124			$5.130124			$121,712,191.90			$139,969,020.69

We estimate expenses payable by us in connection with this offering, other than the underwriting discounts and commissions referred to above, will be approximately $0.55 million.

Listing

Our common shares are listed on the Nasdaq Global Market under the trading symbol “ATAI”.

Stamp Taxes

If you purchase common shares offered in this prospectus, you may be required to pay stamp taxes and other charges under the laws and practices of the country of purchase, in addition to the offering price listed on the cover page of this prospectus supplement.

Option to Purchase Additional Common Shares

We have granted to the underwriters an option, exercisable for 30 days from the date of this prospectus, to purchase, from time to time, in whole or in part, up to an aggregate of 3,558,750 common shares from us at the public offering price set forth on the cover page of this prospectus, less underwriting discounts and commissions. If the underwriters exercise this option, each underwriter will be obligated, subject to specified conditions, to purchase a number of additional common shares proportionate to that underwriter’s initial purchase commitment as indicated in the table above. 

No Sales of Similar Securities

We have agreed, subject to certain exceptions, that we will not, and will not publicly disclose an intention to, during the period ending 90 days after the date of this prospectus supplement, or the Restricted Period, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any common shares or any securities convertible into or exercisable or exchangeable for common shares, (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the common shares, whether any such transaction described in (i) and (ii) above is to be settled by delivery of common shares or such other securities, in cash or otherwise or (iii) file any registration statement with the SEC relating to the offering of any common shares or any securities convertible into or exercisable or exchangeable for common shares, without the prior written consent of Jefferies LLC.

The restrictions set forth above with respect to us do not apply to: (A) the common shares to be sold in this offering, (B) the issuance by us of common shares upon the exercise of an option or warrant or the conversion of a security outstanding on the date of this prospectus supplement as described in this prospectus supplement and the accompanying prospectus, in each case as described hereof, (C) grants of options, restricted stock or other equity awards and the issuance of common shares or securities convertible into or exercisable for common shares (whether upon the exercise of stock options or otherwise) to our employees, officers, directors, advisors, or consultants pursuant to the terms of a plan in effect on the date of this prospectus supplement, (D) the filing of a registration statement on Form S-8 to register common shares issuable pursuant to any employee benefit plans, qualified stock option plans or other employee compensation plans adopted and approved by the Company’s board of directors, (E) facilitating the establishment of a trading plan on behalf of a shareholder, officer or director of ours pursuant to

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Rule 10b5-1 under the Exchange Act, for the transfer of common shares, provided that (i) such plan does not provide for the transfer of common shares during the Restricted Period and (ii) to the extent a public announcement or filing under the Exchange Act, if any, is required of or voluntarily made by the Company regarding the establishment of such plan, such announcement or filing shall include a statement to the effect that no transfer of common shares may be made under such plan during the Restricted Period, (F) the sale or issuance of common shares or securities convertible into or exercisable for common shares in connection with the SPA, (G) the sale or issuance of or entry into an agreement to sell or issue common shares or securities convertible into or exercisable for common shares in connection with any mergers; acquisition of securities, businesses, property, technologies or other assets; joint ventures; strategic alliances, commercial relationships or other collaborations; or the assumption of employee benefit plans in connection with mergers or acquisitions; provided that the aggregate number of common shares or securities convertible into or exercisable for common shares (on an as-converted or as-exercised basis, as the case may be) that the Company may sell or issue or agree to sell or issue pursuant to this clause (G) shall not exceed 10% of the total number of common shares issued and outstanding immediately following the completion of the transactions contemplated by this prospectus supplement (determined on a fully diluted basis and as adjusted for stock splits, stock dividends and other similar events after the date hereof); and provided further, that each recipient of common shares or securities convertible into or exercisable for common shares pursuant to this clause (G) shall, on or prior to such issuance, execute a lock-up agreement respect to the remaining portion of the Restricted Period, (H) the amendment of, or filing of, any prospectus, prospectus supplement or amendment relating to, any “at-the-market” offering program described in the the amendment of, or filing of, such prospectus, prospectus supplement or amendment, or the issuance of common shares pursuant to a placement made under any such program, provided that no shares may be offered or sold pursuant to such program during the period ending upon the earlier of (i) the closing of the green shoe and (ii) 30 days after the date of the prospectus or (I) the filing by the Company of one registration statement on Form S-3 registering the offer and sale of common shares or securities convertible or exercisable into common shares held by certain of our investors to be received by the Sellers pursuant to the SPA, as disclosed in the Current Reports on Form 8-K filed by the Company on June 2, 2025 and July 1, 2025, from time to time.

Pursuant to certain “lock-up” agreements, Apeiron Investment, Ltd. and all of our directors and executive officers have agreed, subject to certain exceptions, that they will not, directly or indirectly (or cause any direct or indirect affiliate to), and will not publicly disclose the intention to, during the Restricted Period (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, any common shares or securities convertible into or exchangeable or exercisable for any common shares (including, without limitation, common shares that may be deemed to be beneficially owned by such director or officer in accordance with the rules and regulations of the SEC, securities which may be issued upon exercise of a stock option or warrant and any common shares, options, warrants or securities now owned or hereafter acquired by such director or officer, or the Lock-Up Securities, (ii) enter into any swap, hedge, option, derivative or other arrangement (including, without limitation, any short sale or the purchase or sale of, or entry into, any put or call option, or combination thereof, forward, swap or any other derivative transaction or instrument, however described or defined) designed or intended to, or which could reasonably be expected to lead to or result in, a sale, loan, pledge or other disposition or transfer of any economic consequences of ownership, in whole or in part, directly or indirectly, of any Lock-Up Securities, whether any such aforementioned transaction is to be settled by delivery of the Lock-Up Securities, in cash or otherwise, or (iii) exercise any right with respect to the registration of any Lock-Up Securities, or file, cause to be filed or cause to be confidentially submitted, any registration statement in connection therewith, under the Securities Act, without the prior written consent of Jefferies LLC.

The restrictions in the “lock-up” agreement set forth above do not apply to parties to the “lock-up” agreements with respect to transfer of Lock-up Securities: (A) acquired in the open market after the completion of this offering, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made in connection with subsequent sales of such Lock-Up Securities acquired in such open market transactions; (B) as a bona fide gift or gifts; (C) to any beneficiary pursuant to a will, other testamentary document or intestate succession to the legal representatives, heirs, beneficiary or immediate family member; (D) to any trust, partnership, limited liability company or other entity for the direct or indirect benefit of such lock-up party or the immediate family thereof; (E) as distributions to limited partners, members or stockholders of such lock-up party; (F) to affiliates or to any investment fund or other entity controlled or managed by such lock-up party; (G) to a nominee or custodian of a person or entity to whom a disposition or transfer would be permissible under clauses (B) through (F) above; (H) transfers pursuant to an order of a court or regulatory agency, including a domestic relations order or negotiated divorce settlement, or to comply with any regulations related to the ownership of common shares; (I) to us or our

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affiliates upon death, disability or termination of employment of such lock-up party; (J) to us or our affiliates (i) deemed to occur upon the cashless exercise of options or convertible debt instruments or (ii) for the primary purpose of paying the exercise price of such options or convertible debt instruments or for paying taxes (including estimated taxes) due as a result of the exercise of such options or as a result of the vesting of common shares under restricted stock units or restricted stock awards, in each case pursuant to employee benefit plans disclosed in our filings with the SEC; (K) pursuant to sales in the open market to satisfy tax withholding (including estimated taxes) due as a result of the vesting of common shares under restricted stock units or restricted stock awards, in each case pursuant to employee benefit plans disclosed in our filings with the SEC; (L) pursuant to a bona fide third-party tender offer, merger, consolidation or other similar transaction made to all holders of the common shares involving a change of control us following the consummation of this offering that has been approved by the Company’s board of directors, provided that in the event that such tender offer, merger, consolidation or other such transaction is not completed, such lock-up party’s common shares shall remain subject to such restrictions and (M) in any pledge, hypothecation or security interest in Lock-Up Securities in a bona fide transaction to a bona-fide third party as collateral or security for any margin loan or other loans, advances or extensions of credit entered into by the undersigned or any of its direct or indirect subsidiaries or affiliates, or the transfer of Lock-Up Securities that have been pledged or hypothecated to a bona-fide third party on or prior to the date of such “lock-up” agreement, in the event of a foreclosure on such common shares pursuant to such pledge or hypothecation, provided that any filing under Section 16 or Section 13 of the Exchange Act shall clearly indicate that the filing relates to the circumstances described in this clause and no other public filing or announcement shall be required or shall be made voluntarily during the Restricted Period in connection with such transfer or disposition; provided that in the case of any transfer or distribution pursuant to clauses (B) through (G) above, (i) each donee, trustee, transferee or distributee, as the case may be, shall sign and deliver a lock-up letter substantially in the form of the “lock-up” agreements and (ii) such transfers are not dispositions for value; in the case of any transfer or distribution pursuant to clauses (C) through (G), each party (donor, donee, trustee, transferor, transferee, distributer or distributee) shall not be required by law (including, without limitation, the disclosure requirements of the Securities Act and the Exchange Act) to make, and shall agree to not voluntarily make, any filing or public announcement of the transfer or disposition prior to the expiration of the Restricted Period; and in the case of any transfer or distribution pursuant to clauses (B) and (H) through (K) above, any filing that is required under the Securities Act or the Exchange Act shall include disclosure explaining the nature of the transfer or disposition in the footnotes thereto, and no filing or public announcement of the transfer or disposition shall be voluntarily made prior to the expiration of the Restricted Period.

Notwithstanding such restrictions in the “lock-up” agreements, a lock-up party may enter into a written trading plan established pursuant to Rule 10b5-1 of the Exchange Act, or a Rule 10b5-1 Plan, during the Restricted Period, provided that no direct or indirect offers, pledges, sales, contracts to sell sales of any option or contract to purchase, purchases of any option or contract to sell, grants of any option, right or warrant to purchase, loans, or other transfers or disposals of any Lock-Up Securities may be effected pursuant to such plan during the Restricted Period; provided further, that neither we nor the lock-up party will voluntarily report the establishment of such Rule 10b5-1 Plan in any public report or filing with the SEC under the Exchange Act during the Restricted Period and any required filing under the Exchange Act regarding such plan indicates that no sales of common shares shall be permitted under such plan during the Restricted Period.

Stabilization

The underwriters have advised us that they may engage in short sale transactions, stabilizing transactions, syndicate covering transactions or the imposition of penalty bids in connection with this offering. These activities may have the effect of stabilizing or maintaining the market price of the common shares at a level above that which might otherwise prevail in the open market. Establishing short sales positions may involve either “covered” short sales or “naked” short sales.

“Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional common shares in this offering. The underwriters may close out any covered short position by either exercising their option to purchase additional of our common shares or purchasing of our common shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the option to purchase additional common shares.

“Naked” short sales are sales in excess of the option to purchase additional of our common shares. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position

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is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our common shares in the open market after pricing that could adversely affect investors who purchase in this offering.

A stabilizing bid is a bid for the purchase of common shares on behalf of the underwriters for the purpose of fixing or maintaining the price of the common shares. A syndicate covering transaction is the bid for or the purchase of common shares on behalf of the underwriters to reduce a short position incurred by the underwriters in connection with the offering. Similar to other purchase transactions, the underwriter’s purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common shares or preventing or retarding a decline in the market price of our common shares. As a result, the price of our common shares may be higher than the price that might otherwise exist in the open market. A penalty bid is an arrangement permitting the underwriters to reclaim the selling concession otherwise accruing to a syndicate member in connection with the offering if the common shares originally sold by such syndicate member are purchased in a syndicate covering transaction and therefore have not been effectively placed by such syndicate member.

Neither we, nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common shares. The underwriters are not obligated to engage in these activities and, if commenced, any of the activities may be discontinued at any time.

The underwriters may also engage in passive market making transactions in our common shares on The NASDAQ Global Market in accordance with Rule 103 of Regulation M during a period before the commencement of offers or sales of shares of our common shares in this offering and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded.

Electronic Distribution

A prospectus in electronic format may be made available by e-mail or on the web sites or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may agree with us to allocate a specific number of common shares for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus in electronic format, the information on the underwriters’ web sites and any information contained in any other web site maintained by any of the underwriters is not part of this prospectus, has not been approved and/or endorsed by us or the underwriters and should not be relied upon by investors.

Other Activities and Relationships

The underwriter and certain of its affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriter and certain of its affiliates have, from time to time, performed, and may in the future perform, various commercial and investment banking and financial advisory services for us and our affiliates, for which they received or will receive customary fees and expenses. For example, Jefferies LLC is the sales agent under the Sales Agreement pursuant to which we may offer and sell, from time to time, our common shares by any method permitted that is deemed an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act.

In the ordinary course of their various business activities, the underwriter and certain of its affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments issued by us and our affiliates. If the underwriters or their respective affiliates have a lending relationship with us, they routinely hedge their credit exposure to us consistent with their customary risk management policies. The underwriters and their respective affiliates may hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities or the securities of our affiliates, including potentially the common shares offered hereby. Any such short positions could adversely affect future trading prices of the common shares offered hereby. The underwriters and certain of their respective affiliates may also communicate independent

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investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Disclaimers About Non-U.S. Jurisdictions

Canada. The common shares may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the common shares must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement and the accompanying prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Switzerland. The securities will not be offered, directly or indirectly, to the public in Switzerland and neither this prospectus supplement nor the accompany prospectus constitutes a public offering prospectus as that term is understood pursuant to article 652a or 1156 of the Swiss Federal Code of Obligations.

European Economic Area. In relation to each Member State of the European Economic Area (each, a “Member State”), no shares have been offered or will be offered pursuant to the offering to the public in that Member State prior to the publication of a prospectus in relation to the shares which has been approved by the competent authority in that Member State or, where appropriate, approved by the competent authority in another Member State and notified to the competent authority in that Member State, all in accordance with the Prospectus Regulation, except that offers of shares may be made to the public in that Member State at any time under the following exemptions under the Prospectus Regulation:

A.
to any legal entity which is a qualified investor as defined under the Prospectus Regulation;

B.
to fewer than 150 natural or legal persons (other than qualified investors as defined under the Prospectus Regulation), subject to obtaining the prior consent of the underwriters; or

C.
in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of shares shall require us or the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation and each person who initially acquires any shares or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with the underwriters and us that it is a “qualified investor” within the meaning of Article 2(e) of the Prospectus Regulation.

In the case of any shares being offered to a financial intermediary as that term is used in the Prospectus Regulation, each such financial intermediary will be deemed to have represented, acknowledged and agreed to and with the underwriters and us that the shares acquired by it in the offer have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any shares to the public other than their offer or resale in a Member State to qualified investors as defined in the Prospectus Regulation or in circumstances in which the prior consent of the underwriters has been obtained to each such proposed offer or resale.

For the purposes of this provision, the expression an “offer to the public” in relation to shares in any Member State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129 (as amended).

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United Kingdom. In addition, in the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Regulation) (i) who have professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order and/or (iii) to whom it may otherwise be lawfully communicated (all such persons together being referred to as “relevant persons”) in circumstances which have not resulted and will not result in an offer to the public of the shares in the United Kingdom within the meaning of the Financial Services and Markets Act 2000.

Any person in the United Kingdom that is not a relevant person should not act or rely on the information included in this document or use it as basis for taking any action. In the United Kingdom, any investment or investment activity that this document relates to may be made or taken exclusively by relevant persons.

France. Neither this prospectus supplement, nor the accompanying prospectus, nor any other offering material relating to the shares described in this prospectus supplement and the accompanying prospectus has been submitted to the clearance procedures of the Autorité des Marchés Financiers or of the competent authority of another member state of the European Economic Area and notified to the Autorité des Marchés Financiers. The shares have not been offered or sold and will not be offered or sold, directly or indirectly, to the public in France. Neither this prospectus supplement, nor the accompanying prospectus, nor any other offering material relating to the shares has been or will be:

• released, issued, distributed or caused to be released, issued or distributed to the public in France; or

• used in connection with any offer for subscription or sale of the shares to the public in France.

Such offers, sales and distributions will be made in France only:

• to qualified investors (investisseurs qualifiés) and/or to a restricted circle of investors (cercle restreint d’investisseurs), in each case investing for their own account, all as defined in, and in accordance with, articles L.411-2, D.411-1, D.411-2, D.734-1, D.744-1, D.754-1 and D.764-1 of the French Code monétaire et financier;

• to investment services providers authorized to engage in portfolio management on behalf of third parties; or

• in a transaction that, in accordance with article L.411-2-II-1"-or-2"-or 3" of the French Code monétaire et financier and article 211-2 of the General Regulations (Règlement Général) of the Autorité des Marchés Financiers, does not constitute a public offer (appel public à l’épargne).

The shares may be resold directly or indirectly, only in compliance with articles L.411-1, L.411-2, L.412-1 and L.621-8 through L.621-8-3 of the French Code monétaire et financier.

Hong Kong. The shares have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (a) to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571 of the Laws of Hong Kong) (the “SFO”) of Hong Kong and any rules made thereunder; or (b) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32) of Hong Kong) (the “CO”), or which do not constitute an offer to the public within the meaning of the CO. No advertisement, invitation or document relating to the shares has been or may be issued or has been or may be in the possession of any person for the purposes of issue, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the SFO and any rules made thereunder.

Germany. Each person who is in possession of this prospectus supplement is aware of the fact that no German securities prospectus (wertpapierprospekt) within the meaning of the German Securities Prospectus Act (Wertpapier-prospektgesetz) (the “German Securities Act”) of the Federal Republic of Germany has been or will be published with respect to the securities. In particular, each underwriter has represented that it has not engaged and has agreed that it will not engage in a public offering in the Federal Republic of Germany within the meaning of the German Securities Act with respect to any of the securities otherwise than in accordance with the German Securities Act and all other applicable legal and regulatory requirements.

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Japan. No registration pursuant to Article 4, paragraph 1 of the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended) (the “FIEL”) has been made or will be made with respect to the solicitation of the application for the acquisition of the shares.

Accordingly, the shares have not been, directly or indirectly, offered or sold and will not be, directly or indirectly, offered or sold in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan) or to others for re-offering or re-sale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan except pursuant to an exemption from the registration requirements, and otherwise in compliance with, the FIEL and the other applicable laws and regulations of Japan.

For Qualified Institutional Investors (“QII”)

Please note that the solicitation for newly-issued securities (as described in Paragraph 2, Article 4 of the FIEL) in relation to the shares constitutes a “QII only private placement” (as described in Paragraph 1, Article 23-13 of the FIEL). Disclosure regarding any such solicitation, as is otherwise prescribed in Paragraph 1, Article 4 of the FIEL, has not been made in relation to the shares. The shares may only be transferred to QIIs.

For Non-QII Investors

Please note that the solicitation for newly-issued securities (as described in Paragraph 2, Article 4 of the FIEL) in relation to the shares constitutes a “small number private placement” (as is described in Paragraph 4, Article 23-13 of the FIEL). Disclosure regarding any such solicitation, as is otherwise prescribed in Paragraph 1, Article 4 of the FIEL, has not been made in relation to the shares. The shares may only be transferred en bloc without subdivision to a single investor.

Singapore. The underwriters have acknowledged that neither this prospectus supplement nor the accompanying prospectus has been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, the underwriters have represented and agreed that it has not offered or sold any shares or caused the shares to be made the subject of an invitation for subscription or purchase and will not offer or sell any shares or cause the shares to be made the subject of an invitation for subscription or purchase, and has not circulated or distributed, nor will it circulate or distribute, this prospectus supplement, the accompanying prospectus or any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares, whether directly or indirectly, to any person in Singapore other than:

A.
to an institutional investor (as defined in Section 4A of the Securities and Futures Act (Chapter 289) of Singapore, as modified or amended from time to time (the “SFA”)) pursuant to Section 274 of the SFA;

B.
to a relevant person (as defined in Section 275(2) of the SFA) pursuant to Section 275(1) of the SFA, or any person pursuant to Section 275(1A) of the SFA, and in accordance with the conditions specified in Section 275 of the SFA; or

C.
otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

A.
a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or

B.
a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary of the trust is an individual who is an accredited investor,

securities or securities-based derivatives contracts (each term as defined in Section 2(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (however described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the shares pursuant to an offer made under Section 275 of the SFA except:

(i)
to an institutional investor or to a relevant person, or to any person arising from an offer referred to in Section 275(1A) or Section 276(4)(i)(B) of the SFA;

(ii)
where no consideration is or will be given for the transfer;

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(iii)
where the transfer is by operation of law;

(iv)
as specified in Section 276(7) of the SFA; or

(v)
as specified in Regulation 37A of the Securities and Futures (Offers of Investments) (Securities and Securities-based Derivatives Contracts) Regulations 2018.

Singapore SFA Product Classification—In connection with Section 309B of the SFA and the CMP Regulations 2018, unless otherwise specified before an offer of shares, we have determined, and hereby notify all relevant persons (as defined in Section 309A(1) of the SFA), that the shares are “prescribed capital markets products” (as defined in the CMP Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products and MAS Notice FAA-N16: Notice on Recommendations on Investment Products).

Australia. Neither this prospectus supplement nor the accompanying prospectus is a disclosure document for the purposes of Australia’s Corporations Act 2001 (Cth) of Australia, or Corporations Act, has not been lodged with the Australian Securities & Investments Commission and is only directed to the categories of exempt persons set out below. Accordingly, if you receive this prospectus supplement and the accompanying prospectus in Australia:

You confirm and warrant that you are either:

• a “sophisticated investor” under section 708(8)(a) or (b) of the Corporations Act;

• a “sophisticated investor” under section 708(8)(c) or (d) of the Corporations Act and that you have provided an accountant’s certificate to the Company which complies with the requirements of section 708(8)(c)(i) or (ii) of the Corporations Act and related regulations before the offer has been made; or

• a “professional investor” within the meaning of section 708(11)(a) or (b) of the Corporations Act.

To the extent that you are unable to confirm or warrant that you are an exempt sophisticated investor or professional investor under the Corporations Act any offer made to you under this prospectus supplement and the accompanying prospectus is void and incapable of acceptance.

You warrant and agree that you will not offer any of the common shares issued to you pursuant to this prospectus supplement and the accompanying prospectus for resale in Australia within 12 months of those securities being issued unless any such resale offer is exempt from the requirement to issue a disclosure document under section 708 of the Corporations Act.

Israel. The shares offered by this prospectus supplement and the accompanying prospectus have not been approved or disapproved by the Israel Securities Authority (the “ISA”), nor have such shares been registered for sale in Israel. The shares may not be offered or sold, directly or indirectly, to the public in Israel, absent the publication of a prospectus that has been approved by the ISA. The ISA has not issued permits, approvals or licenses in connection with this offering or publishing this prospectus supplement or the accompanying prospectus, nor has it authenticated the details included herein, confirmed their reliability or completeness, or rendered an opinion as to the quality of the shares being offered.

This document does not constitute a prospectus under the Israeli Securities Law, 5728-1968 (the “Securities Law”), and has not been filed with or approved by the ISA. In the State of Israel, this document may be distributed only to, and may be directed only at, and any offer of the securities offered hereby is directed only at, (i) to the extent applicable, a limited number of persons in accordance with the Securities Law and (ii) investors listed in the first addendum (the “Addendum”), to the Israeli Securities Law, consisting primarily of joint investment in trust funds, provident funds, insurance companies, banks, portfolio managers, investment advisors, members of the Tel Aviv Stock Exchange Ltd., underwriters, venture capital funds, entities with equity in excess of NIS 50 million and “qualified individuals,” each as defined in the Addendum (as it may be amended from time to time), collectively referred to as qualified investors (in each case purchasing for their own account or, where permitted under the Addendum, for the accounts of their clients who are investors listed in the Addendum). Qualified investors will be required to submit written confirmation that they fall within the scope of the Addendum, are aware of the meaning of same and agree to it.

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People’s Republic of China. This prospectus supplement and the accompanying prospectus have not been and will not be circulated or distributed in the People’s Republic of China, and no securities may be offered or sold, or will be offered or sold, to any person for re-offering or resale, directly or indirectly, to any resident of the People’s Republic of China except pursuant to applicable laws and regulations of the People’s Republic of China.

We have not authorized and do not authorize the making of any offer of securities through any financial intermediary on our behalf, other than offers made by the underwriters and their affiliates, with a view to the final placement of the securities as contemplated in this document. Accordingly, no purchaser of the shares, other than the underwriters, is authorized to make any further offer of shares on our behalf or on behalf of the underwriters.

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LEGAL MATTERS

The validity of our common shares offered hereby and certain other matters of Dutch law will be passed upon for us by NautaDutilh N.V. and certain matters of U.S. federal law will be passed upon for us by Latham & Watkins LLP. Certain legal matters in connection with this offering will be passed upon for the underwriters by Goodwin Procter LLP, with respect to U.S. federal law.

EXPERTS

The financial statements of ATAI Life Sciences N.V. incorporated by reference in this prospectus supplement, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm, given their authority as experts in accounting and auditing.

The audited historical financial statements of Beckley Psytech Limited included in Exhibit 99.1 of ATAI Life Sciences N.V.’s Current Report on Form 8-K, dated September 29, 2025, have been so incorporated in reliance on the report (which contains an explanatory paragraph relating to the Beckley Psytech Limited’s ability to continue as a going concern as described in Note 1 to the financial statements) of PricewaterhouseCoopers LLP, independent auditors, given on the authority of said firm as experts in auditing and accounting.

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PROSPECTUS

ATAI Life Sciences N.V.

Common Shares

Debt Securities

Warrants

Units

Common Shares Offered by the Selling Securityholders,

Including Up to 45,321,301 Common Shares Offered by the Selling Securityholders Named Herein

We may offer and sell the securities identified above, and certain selling securityholders may offer and sell our common shares, nominal value €0.10 per share (“common shares”) (including up to 45,321,301 common shares by the selling securityholders identified in the “selling securityholders” section of this prospectus), in each case from time to time in one or more offerings. This prospectus provides you with a general description of the securities. We will not receive any proceeds from the sale of our common shares by any of the selling securityholders.

Each time we offer and sell securities, we will provide a supplement to this prospectus that contains specific information about the offering and the amounts, prices and terms of the securities. In addition, in connection with certain offers and sales of securities by the selling securityholders, we and the selling securityholders will provide, if applicable, a prospectus supplement to this prospectus containing specific information about the offering by the selling securityholders and the amounts, prices and terms of the securities being offered. The supplement may also add, update or change information contained in this prospectus with respect to that offering. You should carefully read this prospectus and the applicable prospectus supplement before you invest in any of our securities.

We may offer and sell the securities described in this prospectus and any prospectus supplement to or through one or more underwriters, dealers and agents, or directly to purchasers, or through a combination of these methods. In addition, the selling securityholders may offer and sell our common shares from time to time, together or separately. If any underwriters, dealers or agents are involved in the sale of any of the securities, their names and any applicable purchase price, fee, commission or discount arrangement between or among them will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement. See the sections of this prospectus entitled “About this Prospectus” and “Plan of Distribution” for more information. No securities may be sold without delivery of this prospectus and the applicable prospectus supplement describing the method and terms of the offering of such securities.

Investing in our securities involves risks. See the “Risk Factors” on page 8 of this prospectus and any similar section contained in the applicable prospectus supplement concerning factors you should consider before investing in our securities.

Our common shares are listed on the Nasdaq Global Market under the symbol “ATAI.” On September 26, 2025, the last reported sale price of our common shares on the Nasdaq Global Market was $5.27 per share.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is September 29, 2025.

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ABOUT THIS PROSPECTUS			1
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS			2
TRADEMARKS			4
WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE			5
THE COMPANY			7
RISK FACTORS			8
USE OF PROCEEDS			9
DESCRIPTION OF SHARE CAPITAL AND ARTICLES OF ASSOCIATION			10
DESCRIPTION OF DEBT SECURITIES			16
DESCRIPTION OF WARRANTS			23
DESCRIPTION OF UNITS			24
GLOBAL SECURITIES			25
SELLING SECURITYHOLDERS			28
PLAN OF DISTRIBUTION			30
LEGAL MATTERS			33
EXPERTS			33

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the U.S. Securities and Exchange Commission, or the SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”), using a “shelf” registration process. By using a shelf registration statement, we may sell securities from time to time and in one or more offerings and the selling securityholders identified herein, including, if applicable, their respective donees, pledgees, transferees, assignees, designees, distributees or other successors-in-interest who after the date of this prospectus come to hold any of the interests of any of such selling securityholders’ respective interests in our common shares other than through a public sale, and to be identified in a supplement to this prospectus may, from time to time, sell our common shares, including up to 45,321,301 common shares by the selling securityholders identified in the “selling securityholders” section of this prospectus, from time to time in one or more offerings as described in this prospectus. Each time that we or the selling securityholders offer and sell securities, we or the selling securityholders will provide a prospectus supplement to this prospectus that contains specific information about the securities being offered and sold and the specific terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement or free writing prospectus may also add, update or change information contained in this prospectus with respect to that offering. If there is any inconsistency between the information in this prospectus and the applicable prospectus supplement or free writing prospectus, you should rely on the prospectus supplement or free writing prospectus, as applicable. Before purchasing any securities, you should carefully read both this prospectus and the applicable prospectus supplement (and any applicable free writing prospectuses), together with the additional information described under the heading “Where You Can Find More Information; Incorporation by Reference.”

Neither we, nor the selling securityholders, have authorized anyone to provide you with any information or to make any representations other than those contained in this prospectus, any applicable prospectus supplement or any free writing prospectuses prepared by or on behalf of us or to which we have referred you. We and the selling securityholders take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We and the selling securityholders will not make an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus and the applicable prospectus supplement to this prospectus is accurate only as of the date on its respective cover, that the information appearing in any applicable free writing prospectus is accurate only as of the date of that free writing prospectus, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, unless we indicate otherwise. Our business, financial condition, results of operations and prospects may have changed since those dates. This prospectus incorporates by reference, and any prospectus supplement or free writing prospectus may contain and incorporate by reference, market data and industry statistics and forecasts that are based on independent industry publications and other publicly available information. Although we believe these sources are reliable, we do not guarantee the accuracy or completeness of this information and we have not independently verified this information. In addition, the market and industry data and forecasts that may be included or incorporated by reference in this prospectus, any prospectus supplement or any applicable free writing prospectus may involve estimates, assumptions and other risks and uncertainties and are subject to change based on various factors, including those discussed under the heading “Risk Factors” contained in this prospectus, the applicable prospectus supplement and any applicable free writing prospectus, and under similar headings in other documents that are incorporated by reference into this prospectus. Accordingly, investors should not place undue reliance on this information.

Unless the context otherwise requires, all references in this prospectus to “atai,” “we,” “our,” “us” or the “Company,” refer to ATAI Life Sciences N.V. and its consolidated subsidiaries. When we refer to “you,” we mean the potential holders of the applicable series of securities.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. We intend such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). All statements contained in this prospectus other than statements of historical fact are forward-looking statements, including without limitation statements regarding our future operating results and financial position; the success, cost, and timing of development of our product candidates, including the progress of preclinical studies and clinical trials and related milestones; the commercialization of our current product candidates and any other product candidates we may identify and pursue, if approved, including our ability to successfully build a specialty sales force and commercial infrastructure to market our current product candidates and any other product candidates we may identify and pursue; the timing of and our ability to obtain and maintain regulatory approvals; our business strategy and plans, including the benefits of our corporate restructuring and our pending corporate redomiciliation to the U.S.; potential acquisitions, partnerships and other strategic arrangements, including our pending transaction with Beckley Psytech Limited (“Beckley Psytech”); the ability to generate revenue from any current or future licensing agreements and other strategic arrangements, the sufficiency of our cash and cash equivalents and short-term securities to fund our operations; and the plans and objectives of management for future operations and capital expenditures. The words “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “expect,” “could,” “would,” “project,” “plan,” “potentially,” “preliminary,” “likely,” and similar expressions are intended to identify forward-looking statements.

We have based these forward-looking statements largely on our current expectations and projections about future events and trends that we believe may affect our financial condition, results of operations, business strategy, short-term and long-term business operations and objectives, and financial needs. These forward-looking statements are neither promises nor guarantees, and are subject to a number of important factors that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation: we are a clinical-stage biopharmaceutical company and have incurred significant losses since our inception, and we expect to incur losses for the foreseeable future and may never be profitable; if we are unable to obtain funding when needed and on acceptable terms, we could be forced to delay, limit or discontinue our product candidate development efforts; our limited operating history may make it difficult for you to evaluate the success of our business and to assess our future viability; risks related to the proposed transaction with Beckley Psytech; we rely on third parties to assist in conducting our clinical trials and some aspects of our research and preclinical testing; we currently rely on qualified therapists working at third-party clinical trial sites to administer certain of our product candidates in our clinical trials and we expect this to continue upon approval, if any, of our current or future product candidates, and if third-party sites fail to recruit and retain a sufficient number of therapists or effectively manage their therapists, our business, financial condition and results of operations would be materially harmed; our product candidates are in preclinical or clinical development, which is a lengthy and expensive process with uncertain outcomes, and we cannot give any assurance that any of our product candidates will be successfully developed and/or receive regulatory approval, which is necessary before they can be commercialized; research and development of drugs targeting the central nervous system, or CNS, is particularly difficult, and it can be difficult to predict and understand why a drug has a positive effect on some patients but not others, which may reduce the likelihood our product candidates are ultimately approved and therefore may have a material adverse effect on our business and operating results; the production and sale of our product candidates may be considered illegal or may otherwise be restricted due to the use of controlled substances, which may also have consequences for the legality of investments from foreign jurisdictions and therefore we may not be successful in commercializing our product candidates in such jurisdictions, which will adversely affect our business, financial condition and results of operations; we face significant competition in an environment of rapid technological and scientific change, and there is a possibility that our competitors may achieve regulatory approval before we do or develop therapies that are safer, more advanced or more effective than ours, which may negatively impact our ability to successfully market or commercialize any product candidates we may develop and ultimately harm our financial condition; if we are unable to obtain and maintain sufficient intellectual property protection for our existing product candidates or any other product candidates that we may identify, or if the scope of the intellectual property protection we currently have or obtain in the future is not sufficiently broad, our competitors could develop and commercialize product candidates similar or identical to ours, and our ability to successfully commercialize our existing product candidates and any other product candidates that we may pursue may be impaired; third parties may claim that we are infringing, misappropriating or otherwise violating their intellectual property rights, the outcome of which would be uncertain and may prevent or delay our development and commercialization efforts; our future success depends on our ability

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to retain key employees, directors, consultants and advisors and to attract, retain and motivate qualified personnel; if we fail to maintain an effective system of disclosure controls and internal control over financial reporting our ability to produce timely and accurate financial statements or comply with applicable regulations could be impaired; our business is subject to economic, political, regulatory and other risks associated with international operations; a pandemic, epidemic, or outbreak of an infectious disease, such as the COVID-19 pandemic, may materially and adversely affect our business, including our preclinical studies, clinical trials, trial sites, third parties on whom we rely, our supply chain, our ability to raise capital, our ability to conduct regular business and our financial results, and other risks, uncertainties, and assumptions described under “Risk Factors” in Item 1A of Part I, “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in Item 7 of Part II and elsewhere in our Form 10-K for the year ended December 31, 2024, as further updated in “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in Item 2 of our Form 10-Q for the quarterly period ended June 30, 2025, and in our subsequent filings with the SEC.

Any forward-looking statements made herein speak only as of the date of this prospectus, and you should not rely on forward-looking statements as predictions of future events. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee that the future results, performance, or achievements reflected in the forward-looking statements will be achieved or will occur. Except as required by applicable law, we undertake no obligation to update any of these forward-looking statements for any reason after the date of this prospectus or to conform these statements to actual results or revised expectations.

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TRADEMARKS

We have proprietary rights to trademarks used in this prospectus that are important to our business, many of which are registered under applicable intellectual property laws. Solely for convenience, trademarks and trade names referred to in this prospectus may appear without the “®” or “™” symbols, but such references are not intended to indicate, in any way, that we will not assert, to the fullest extent possible under applicable law, our rights or the rights of the applicable licensor to these trademarks and trade names. We do not intend our use or display of other companies’ trademarks, trade names or service marks to imply a relationship with, or endorsement or sponsorship of us by, any other companies. Each trademark, trade name or service mark of any other company appearing in this prospectus is the property of its respective holder.

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WHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE

Available Information

We file reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information about issuers, such as us, who file electronically with the SEC. The address of that website is https://www.sec.gov.

Our website address is https://atai.com. The information contained on, or that can be accessed from, our website is not, and should not be deemed to be, a part of this prospectus.

This prospectus and any prospectus supplement are part of a registration statement that we filed with the SEC and do not contain all of the information in the registration statement. The full registration statement may be obtained from the SEC or us, as provided below. Forms of the indenture and other documents establishing the terms of the offered securities are or may be filed as exhibits to the registration statement or documents incorporated by reference in the registration statement. Statements in this prospectus or any prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement through the SEC’s website, as provided above.

Incorporation by Reference

The SEC’s rules allow us to “incorporate by reference” information into this prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is deemed to be part of this prospectus, and subsequent information that we file with the SEC will automatically update and supersede that information. Any statement contained in this prospectus or a previously filed document incorporated by reference will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or a subsequently filed document incorporated by reference modifies or replaces that statement.

This prospectus and any accompanying prospectus supplement incorporate by reference the documents set forth below that have previously been filed with the SEC, but excluding any information furnished to, rather than filed with, the SEC:

• Our Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on March 17, 2025.

• The information specifically incorporated by reference into our Annual Report on Form 10-K from our Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 21, 2025.

• Our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2025, and June 30, 2025, filed with the SEC on May 14, 2025 and on August 14, 2025, respectively.

• Our Current Reports on Form 8-K filed with the SEC on January 10, 2025, January 24, 2025, February 13, 2025, April 30, 2025, May 8, 2025, May 21, 2025, June 2, 2025, July 1, 2025, September 23, 2025 and September 29, 2025.

• The description of our Share Capital contained in our Registration Statement on Form 8-A, filed with the SEC on June 14, 2021 and any amendment or report filed with the SEC for the purpose of updating the description.

All reports and other documents we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, which we refer to as the “Exchange Act” in this prospectus, prior to the termination of this offering but excluding any information furnished to, rather than filed with, the SEC, will also be incorporated by reference into this prospectus and deemed to be part of this prospectus from the date of the filing of such reports and documents.

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You may request a free copy of any of the documents incorporated by reference in this prospectus by writing or telephoning us at the following address:

Attention: Secretary

ATAI Life Sciences N.V.

Prof. J.H. Bavincklaan 7

1183 AT Amstelveen

The Netherlands

+31 20 793 2536

Exhibits to the filings will not be sent, however, unless those exhibits have specifically been incorporated by reference in this prospectus or any accompanying prospectus supplement.

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THE COMPANY

Overview

We are a clinical-stage biopharmaceutical company on a mission to develop highly effective mental health treatments to transform patient outcomes. Founded in 2018, atai emerged from the urgent need for better mental health solutions for patients who are under-served by current treatment options. We are advancing a pipeline of product candidates designed to address the complex nature of mental health disorders. We believe that these investigational compounds have the potential to become rapid-acting, durable, and commercially scalable therapies for mental health patients in need of new treatment options.

Mental health disorders are highly prevalent and estimated to affect more than one billion people globally. The economic burden of these disorders is substantial and growing rapidly. Between 2009 and 2019, spending on mental health care in the United States increased by more than 50%, reaching $225 billion, and a Lancet Commission report estimates that the global economic cost will reach $16 trillion by 2030. While current treatments, such as selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors are well established and effective for certain patients, approximately 65% of patients do not achieve remission of their symptoms after up to four antidepressant treatment trials, translating to a significant unmet medical need.

Corporate Information

The statutory seat of ATAI Life Sciences N.V. is in Amsterdam, the Netherlands. Our office address and our principal executive office is located at Prof. J.H. Bavincklaan 7, 1183 AT Amstelveen, the Netherlands, and our telephone number is +31 20 793 2536. Our website address is https://atai.com. The information contained on, or that can be accessed from, our website does not form part of this document. References to our website address do not constitute incorporation by reference of the information contained on the website, and the information contained on the website is not part of this document or any other document that we file with or furnish to the Securities and Exchange Commission.

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RISK FACTORS

Investment in any securities offered pursuant to this prospectus and the applicable prospectus supplement involves risks. Before deciding whether to invest in our securities, you should carefully consider the risk factors incorporated by reference to our most recent Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K, and all other information contained or incorporated by reference into this prospectus, as updated by our subsequent filings under the Exchange Act, and the risk factors and other information contained in the applicable prospectus supplement and any applicable free writing prospectus. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our securities to decline, resulting in a loss of all or part of your investment. Please also carefully read the section entitled “Cautionary Note Regarding Forward-Looking Statements” included in our most recent Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K. For more information about our SEC filings, please see “Where You Can Find More Information; Incorporation by Reference.”

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USE OF PROCEEDS

We intend to use the net proceeds from the sale of the securities as set forth in the applicable prospectus supplement. We will not receive any of the proceeds from the sale of common shares being offered by any of the selling securityholders.

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DESCRIPTION OF SHARE CAPITAL AND ARTICLES OF ASSOCIATION

The following description of our share capital, certain material provisions of our articles of association and relevant portions of Dutch law is not complete and may not contain all the information you should consider before investing in our share capital. This description is summarized from, and qualified in its entirety by reference to, our articles of association, which have been publicly filed with the SEC. See “Where You Can Find More Information; Incorporation by Reference.” This summary does not constitute legal advice regarding those matters and should not be regarded as such.

General

We are a Dutch a public company (naamloze vennootschap). Our corporate affairs are governed by the provisions of our articles of association, our corporate governance guidelines, our other internal rules, regulations and policies, as amended and restated from time to time, and by the provisions of applicable Dutch law. As provided in our articles of association, subject to Dutch law, we have full capacity to carry on or undertake any business or activity, do any act or enter into any transaction consistent with the objects specified in our articles of association, and, for such purposes, full rights, powers and privileges.

Share Capital

Under Dutch law, our authorized share capital is the maximum capital that we may issue without amending our articles of association. An amendment of our articles of association would require a resolution of the general meeting upon proposal by our board of directors. As of June 30, 2025, our authorized share capital amounted to €75,000,000, consisting of 750,000,000 shares, each with a nominal value of €0.10.

Common Shares

The following summarizes the main rights of holders of our common shares:

• each holder of common shares is entitled to one vote per share on all matters to be voted on by shareholders generally, including the appointment of directors;

• there are no cumulative voting rights;

• the holders of our common shares are entitled to dividends and other distributions as may be declared from time to time by us out of funds legally available for that purpose, if any;

• upon our liquidation and dissolution, the holders of common shares will be entitled to share ratably in the distribution of all of our assets remaining available for distribution after satisfaction of all our liabilities; and

• the holders of our ordinary shares have pre-emption rights in case of share issuances or the grant of rights to subscribe for shares, except if such rights are limited or excluded by the corporate body authorized to do so and except in such cases as provided by Dutch law and our articles of association.

Shareholders’ Register

Pursuant to Dutch law and our articles of association, we must keep our shareholders’ register accurate and current. Our board of directors keeps our shareholders’ register and records names and addresses of all holders of registered shares, showing the date on which the shares were acquired, the date of the acknowledgement by or notification of us as well as the amount paid on each share. The register also includes the names and addresses of those with a right of usufruct (vruchtgebruik) on registered shares belonging to another or a pledge (pandrecht) in respect of such shares. Our common shares shall be in registered form (op naam). We may issue share certificates (aandeelbewijzen) for registered shares in such form as may be approved by our board of directors.

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Corporate Objectives

Pursuant to our articles of association, our main corporate objectives are:

• to worldwide develop biotech companies by utilizing a decentralized, technology and data-driven platform model to serve millions of people suffering from mental illness;

• to acquire and efficiently develop innovative treatments that meet significant unmet medical needs and that lead to paradigm shifts in the field of mental health;

• to incorporate, to participate in, to finance, to hold any other interest in and to conduct the management or supervision of other entities, companies, partnerships and businesses;

• to acquire, to manage, to invest, to exploit, to encumber and to dispose of assets and liabilities;

• to furnish guarantees, to provide security, to warrant performance in any other way and to assume liability, whether jointly and severally or otherwise, in respect of obligations of Group Companies or other parties; and

• to do anything which, in the widest sense, is connected with or may be conducive to the objects described above.

Limitations on the Rights to Own Securities

Our common shares may be issued to individuals, corporations, trusts, estates of deceased individuals, partnerships and unincorporated associations of persons. Our articles of association contain no limitation on the rights to own our shares and no limitation on the rights of non-residents of the Netherlands or foreign shareholders to hold or exercise voting rights.

Limitation on Liability and Indemnification Matters

Under Dutch law, our directors may be held liable for damages in the event of improper or negligent performance of their duties. They may be held liable for damages to our company and to third parties for infringement of our articles of association or of certain provisions of Dutch law. In certain circumstances, they may also incur other specific civil and criminal liabilities. Subject to certain exceptions, our articles of association provide for indemnification of our current and former directors and other current and former officers and employees as designated by our board of directors. No indemnification under our articles of association shall be given to an indemnified person:

• if a competent court or arbitral tribunal has established, without having (or no longer having) the possibility for appeal, that the acts or omissions of such indemnified person that led to the financial losses, damages, expenses, suit, claim, action or legal proceedings as described above are of an unlawful nature (including acts or omissions which are considered to constitute malice, gross negligence, intentional recklessness and/or serious culpability attributable to such indemnified person);

• to the extent that his or her financial losses, damages and expenses are covered under insurance and the relevant insurer has settled, or has provided reimbursement for, these financial losses, damages and expenses (or has irrevocably undertaken to do so);

• in relation to proceedings brought by such indemnified person against our company, except for proceedings brought to enforce indemnification to which he or she is entitled pursuant to our articles of association, pursuant to an agreement between such indemnified person and our company which has been approved by our board of directors or pursuant to insurance taken out by our company for the benefit of such indemnified person; and

• for any financial losses, damages or expenses incurred in connection with a settlement of any proceedings effected without our prior consent.

Under our articles of association, our board of directors may stipulate additional terms, conditions and restrictions in relation to the indemnification described above.

Federal Forum Provision

Our articles of association provide that, unless we consent in writing to the selection of an alternative forum, the sole and exclusive forum for any complaint asserting a cause of action arising under the U.S. Securities Act of 1933, as amended, to the fullest extent permitted by applicable law, shall be the U.S. federal district courts.

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Shareholders’ Meetings

General meetings must be held in the Netherlands, in any of the locations specified in our articles of association. The annual general meeting must be held within six months of the end of each financial year. Additional extraordinary general meetings may also be held, whenever considered appropriate by our board of directors and shall be held within three months after our board of directors has considered it to be likely that our shareholders’ equity (eigen vermogen) has decreased to an amount equal to or lower than half of our paid-in and called up share capital, in order to discuss the measures to be taken if so required.

Pursuant to Dutch law, one or more shareholders or others with meeting rights under Dutch law who jointly represent at least one-tenth of our issued share capital may request us to convene a general meeting, setting out in detail the matters to be discussed. If we have not taken the steps necessary to ensure that such meeting can be held within six weeks after the request, the proponent(s) may, on their application, be authorized by the competent Dutch court in preliminary relief proceedings to convene a general meeting. The court shall disallow the application if it does not appear that the proponent(s) has/have previously requested our board of directors to convene a general meeting and our board of directors has not taken the necessary steps so that the general meeting could be held within six weeks after the request. The application shall also be disallowed if the proponent(s) has/have not demonstrated to have a reasonable interest in the convening of the general meeting.

General meetings must be convened by an announcement published in a Dutch daily newspaper with national distribution. The notice must state the agenda, the time and place of the meeting, the record date (if any), the procedure for participating in the general meeting by proxy, as well as other information as required by Dutch law. The notice must be given at least 15 calendar days prior to the day of the meeting. The agenda for the annual general meeting shall include, among other things, the adoption of our statutory annual accounts, appropriation of our profits and proposals relating to the composition of our board of directors, including the filling of any vacancies. In addition, the agenda shall include such items as have been included therein by our board of directors. The agenda shall also include such items requested by one or more shareholders or others with meeting rights under Dutch law representing at least 3% of our issued share capital. These requests must be made in writing or by electronic means and received by us at least 60 days before the day of the meeting. No resolutions shall be adopted on items other than those that have been included in the agenda.

In accordance with the Dutch Corporate Governance Code (“DCGC), shareholders who have the right to put an item on the agenda for our general meeting or to request the convening of a general meeting shall not exercise such rights until after they have consulted our board of directors. If exercising such rights may result in a change in our strategy (for example, through the dismissal of one or more of our directors), our board of directors must be given the opportunity to invoke a reasonable period of up to 180 days to respond to the shareholders’ intentions. If invoked, our board of directors must use such response period for further deliberation and constructive consultation, in any event with the shareholder(s) concerned and exploring alternatives. At the end of the response time, our board of directors shall report on this consultation and the exploration of alternatives to our general meeting. The response period may be invoked only once for any given general meeting and shall not apply (i) in respect of a matter for which either a response period or a statutory cooling-off period (as discussed below) has been previously invoked or (ii) in situations where a shareholder holds at least 75% of our issued share capital as a consequence of a successful public bid.

Moreover, our board of directors can invoke a cooling-off period of up to 250 days when shareholders, using their right to have items added to the agenda for a general meeting or their right to request a general meeting, propose an agenda item for our general meeting to dismiss, suspend or appoint one or more directors (or to amend any provision in our articles of association dealing with those matters) or when a public offer for our company is made or announced without our support, provided, in each case, that our board of directors believes that such proposal or offer materially conflicts with the interests of our company and its business. During a cooling-off period, our general meeting cannot dismiss, suspend or appoint directors (or amend the provisions in our articles of association dealing with those matters) except at the proposal of our board of directors. During a cooling-off period, our board of directors must gather all relevant information necessary for a careful decision-making process and at least consult with shareholders representing 3% or more of our issued share capital at the time the cooling-off period was invoked, as well as with our Dutch works council (if we or, under certain circumstances, any of our subsidiaries would have one). Formal statements expressed by these stakeholders during such consultations must be published on our website to the extent these stakeholders have approved that publication. Ultimately one week following the last day of the cooling-off period, our board of directors must publish a report in respect of its policy and conduct of affairs during the cooling-off period on our website. This report must remain available for inspection by shareholders and others

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with meeting rights under Dutch law at our office and must be tabled for discussion at the next general meeting. Shareholders representing at least 3% of our issued share capital may request the Enterprise Chamber for early termination of the cooling-off period. The Enterprise Chamber must rule in favor of the request if the shareholders can demonstrate that:

• our board of directors, in light of the circumstances at hand when the cooling-off period was invoked, could not reasonably have concluded that the relevant proposal or hostile offer constituted a material conflict with the interests of our company and its business;

• our board of directors cannot reasonably believe that a continuation of the cooling-off period would contribute to careful policy-making; or

• other defensive measures, having the same purpose, nature and scope as the cooling-off period, have been activated during the cooling-off period and have not since been terminated or suspended within a reasonable period at the relevant shareholders’ request (i.e., no ‘stacking’ of defensive measures).

The general meeting is presided over by the chairperson of our board of directors. If no chairperson has been elected or if he or she is not present at the meeting, the general meeting shall be presided over by the vice-chairperson of our board of directors. If no vice-chairperson has been elected or if he or she is not present at the meeting, the general meeting shall be presided over by another person designated in accordance with our articles of association. Our directors may always attend a general meeting. In these meetings, they have an advisory vote. The chairperson of the meeting may decide at his or her discretion to admit other persons to the meeting.

All shareholders and others with meeting rights under Dutch law are authorized to attend the general meeting, to address the meeting and, in so far as they have such right, to vote pro rata to his or her shareholding. Shareholders may exercise these rights, if they are the holders of shares on the record date, if any, as required by Dutch law, which is currently the 28th day before the day of the general meeting. Under our articles of association, shareholders and others with meeting rights under Dutch law must notify us in writing or by electronic means of their identity and intention to attend the general meeting. This notice must be received by us ultimately on the seventh day prior to the general meeting, unless indicated otherwise when such meeting is convened.

Each ordinary share confers the right on the holder to cast one vote at the general meeting. Shareholders may vote by proxy. No votes may be cast at a general meeting on shares held by us or our subsidiaries or on shares for which we or our subsidiaries hold depository receipts. Nonetheless, the holders of a right of usufruct (vruchtgebruik) and the holders of a right of pledge (pandrecht) in respect of shares held by us or our subsidiaries in our share capital are not excluded from the right to vote on such shares, if the right of usufruct (vruchtgebruik) or the right of pledge (pandrecht) was granted prior to the time such shares were acquired by us or any of our subsidiaries. Neither we nor any of our subsidiaries may cast votes in respect of a share on which we or such subsidiary holds a right of usufruct (vruchtgebruik) or a right of pledge (pandrecht). Shares which are not entitled to voting rights pursuant to the preceding sentences will not be taken into account for the purpose of determining the number of shareholders that vote and that are present or represented, or the amount of the share capital that is provided or that is represented at a general meeting.

Decisions of the general meeting are taken by a simple majority of votes cast, except where Dutch law or our articles of association provide for a qualified majority or unanimity. Subject to any provision of mandatory Dutch law and any higher quorum requirement stipulated by our articles of association, if we would be subject to the requirement that our general meeting can only pass resolutions if a certain part of our issued share capital is present or represented at such general meeting under applicable securities laws or listing rules, then such resolutions shall be subject to such quorum as specified by such securities laws or listing rules pursuant to our articles of association. At the date of this prospectus, applicable securities and listing rules require that any general meeting we hold will require a quorum of 33 1/3 % of the outstanding ordinary shares.

Directors

Appointment of Directors

Our directors are appointed by the general meeting upon binding nomination by our board of directors. However, the general meeting may at all times overrule a binding nomination by a resolution adopted by at least a two-thirds majority of the votes cast, provided such majority represents more than half of the issued share capital. If the general meeting overrules a binding nomination, our board of directors shall make a new nomination.

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At a general meeting, a resolution to appoint a director can only be passed in respect of candidates whose names are stated for that purpose in the agenda of that general meeting or in the explanatory notes thereto.

Our board of directors has adopted a profile for the composition of our non-executive directors. Our board of directors shall make any nomination for the appointment of a director with due regard to the rules and principles set forth in our corporate governance guidelines and this profile, as applicable.

Duties and Liabilities of Directors

Under Dutch law, our board of directors is charged with the management of the company, which includes setting the company’s policies and strategy, subject to the restrictions contained in our articles of association. Our executive directors manage our day-to-day business and operations and implement our strategy. Our non-executive directors focus on the supervision on the policy and functioning of the performance of the duties of all of our directors and our general state of affairs. Our directors may divide their tasks among themselves in or pursuant to internal rules. Each directors has a statutory duty to act in the corporate interest of our company and its business. Under Dutch law, the corporate interest extends to the interests of all corporate stakeholders, such as shareholders, creditors, employees, customers and suppliers. The duty to act in the corporate interest of our company also applies in the event of a proposed sale or break-up of our company, provided that the circumstances generally dictate how such duty is to be applied and how the respective interests of various groups of stakeholders should be weighed.

Our board of directors is entitled to represent our company. The power to represent our company also vests in our Chief Executive Officer, as well as in any other two executive directors acting jointly.

Dividends and Other Distributions

Dividends

Under Dutch law, we may only pay dividends and other distributions from our reserves to the extent our shareholders’ equity (eigen vermogen) exceeds the sum of our paid-in and called-up share capital plus the reserves we must maintain under Dutch law or our articles of association and (if it concerns a distribution of profits) after adoption of our statutory annual accounts by our general meeting from which it appears that such dividend distribution is allowed.

Under our articles of association as they will read upon the date of this prospectus, our board of directors may decide that all or part of the profits shown in our adopted statutory annual accounts will be added to our reserves. After reservation of any such profits, any remaining profits will be at the disposal of the general meeting at the proposal of our board of directors for distribution on our ordinary shares, subject to applicable restrictions of Dutch law. Our board of directors is permitted, subject to certain requirements and applicable restrictions of Dutch law, to declare interim dividends without the approval of our general meeting. Dividends and other distributions shall be made payable no later than a date determined by us. Claims to dividends and other distributions not made within five years from the date that such dividends or distributions became payable will lapse and any such amounts will be considered to have been forfeited to us (verjaring).

Exchange Controls

Under Dutch law, there are no exchange controls applicable to the transfer to persons outside of the Netherlands of dividends or other distributions with respect to, or of the proceeds from the sale of, shares of a Dutch company, subject to applicable restrictions under sanctions and measures, including those concerning export control, pursuant to European Union regulations, the Sanctions Act 1977 (Sanctiewet 1977) or other legislation, applicable anti-boycott regulations, applicable anti-money-laundering regulations and similar rules and provided that, under certain circumstances, payments of such dividends or other distributions must be reported to the Dutch Central Bank at their request for statistical purposes. There are no special restrictions in our articles of association or Dutch law that limit the right of shareholders who are not citizens or residents of the Netherlands to hold or vote shares.

Squeeze-Out Procedures

A shareholder who holds at least 95% of our issued share capital for his or her own account, alone or together with group companies, may initiate proceedings against our other shareholders jointly for the transfer of their shares to such shareholder. The proceedings are held before the Enterprise Chamber and can be instituted by means of a writ of summons served upon each of the other shareholders in accordance with the provisions of the Dutch Code of Civil

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Procedure (Wetboek van Burgerlijke Rechtsvordering). The Enterprise Chamber may grant the claim for squeeze-out in relation to the other shareholders and will determine the price to be paid for the shares, if necessary, after appointment of one or three experts who will offer an opinion to the Enterprise Chamber on the value to be paid for the shares of the other shareholders. Once the order to transfer becomes final before the Enterprise Chamber, the person acquiring the shares shall give written notice of the date and place of payment and the price to the holders of the shares to be acquired whose addresses are known to him. Unless the addresses of all of them are known to the acquiring person, such person is required to publish the same in a daily newspaper with a national circulation.

Dissolution and Liquidation

Under our articles of association, we may be dissolved by a resolution of the general meeting, subject to a proposal of our board of directors. In the event of a dissolution, the liquidation shall be effected by our board of directors, unless our general meeting decides otherwise. During liquidation, the provisions of our articles of association will remain in force as far as possible. To the extent that any assets remain after payment of all of our liabilities, any remaining assets shall be distributed to our shareholders in proportion to their number of shares.

Dutch Corporate Governance Code

As a listed Dutch public company (naamloze vennootschap), we will be subject to the DCGC. The DCGC contains principles and best practice provisions on corporate governance that regulate relations between the board of directors and the general meeting and matters in respect of financial reporting, auditors, disclosure, compliance and enforcement standards. The DCGC is based on a “comply or explain” principle. Accordingly, companies must disclose in their statutory annual reports whether they comply with the provisions of the DCGC. If a company subject to the DCGC does not comply with those provisions, that company would be required to give the reasons for such non-compliance.

We do not comply with best practice provisions of the DCGC, including in order to follow market practice or governance practices in the United States.

Dutch Financial Reporting Supervision Act

On the basis of the Dutch Financial Reporting Supervision Act (Wet toezicht financiële verslaggeving), or the FRSA, the Dutch Authority for the Financial Markets (Stichting Autoriteit Financiële Markten), or AFM, supervises the application of financial reporting standards by Dutch companies whose securities are listed on a Dutch or foreign stock exchange.

Pursuant to the FRSA, the AFM has an independent right to (i) request an explanation from us regarding our application of the applicable financial reporting standards if, based on publicly known facts or circumstances, it has reason to doubt that our financial reporting meets such standards and (ii) recommend to us the making available of further explanations. If we do not comply with such a request or recommendation, the AFM may request that the Enterprise Chamber order us to (i) make available further explanations as recommended by the AFM, (ii) provide an explanation of the way we have applied the applicable financial reporting standards to our financial reports or (iii) prepare or restate our financial reports in accordance with the Enterprise Chamber’s orders.

Listing

Our common shares are listed on the Nasdaq Global Market under the symbol “ATAI.”

Transfer Agent and Registrar

The transfer agent and registrar for our common shares is Computershare Trust Company, N.A.

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DESCRIPTION OF DEBT SECURITIES

The following description, together with the additional information we include in any applicable prospectus supplement or free writing prospectus, summarizes certain general terms and provisions of the debt securities that we may offer under this prospectus. When we offer to sell a particular series of debt securities, we will describe the specific terms of the series in a supplement to this prospectus. We will also indicate in the supplement to what extent the general terms and provisions described in this prospectus apply to a particular series of debt securities.

We may issue debt securities either separately, or together with, or upon the conversion or exercise of or in exchange for, other securities described in this prospectus. Debt securities may be our senior, senior subordinated or subordinated obligations and, unless otherwise specified in a supplement to this prospectus, the debt securities will be our direct, unsecured obligations and may be issued in one or more series.

The debt securities will be issued under an indenture between us and a trustee. We have summarized select portions of the indenture below. The summary is not complete. The form of the indenture has been filed as an exhibit to the registration statement and you should read the indenture for provisions that may be important to you. In the summary below, we have included references to the section numbers of the indenture so that you can easily locate these provisions. Capitalized terms used in the summary and not defined herein have the meanings specified in the indenture.

As used in this section only, “atai” “we,” “our” or “us” refer to ATAI Life Sciences N.V. excluding our subsidiaries, unless expressly stated or the context otherwise requires.

General

The terms of each series of debt securities will be established by or pursuant to resolutions of our board of directors and set forth or determined in the manner provided in resolutions of our board of directors, in an officer’s certificate or by a supplemental indenture. (Section 2.2) The particular terms of each series of debt securities will be described in a prospectus supplement relating to such series (including any pricing supplement or term sheet).

We can issue an unlimited amount of debt securities under the indenture that may be in one or more series with the same or various maturities, at par, at a premium, or at a discount. (Section 2.1) We will set forth in a prospectus supplement (including any pricing supplement or term sheet) relating to any series of debt securities being offered, the aggregate principal amount and the following terms of the debt securities, if applicable:

• the title and ranking of the debt securities (including the terms of any subordination provisions);

• the price or prices (expressed as a percentage of the principal amount) at which we will sell the debt securities;

• any limit on the aggregate principal amount of the debt securities;

• the date or dates on which the principal of the securities of the series is payable;

• the rate or rates (which may be fixed or variable) per annum or the method used to determine the rate or rates (including any commodity, commodity index, stock exchange index or financial index) at which the debt securities will bear interest, the date or dates from which interest will accrue, the date or dates on which interest will commence and be payable and any regular record date for the interest payable on any interest payment date;

• the place or places where principal of, and interest, if any, on the debt securities will be payable (and the method of such payment), where the securities of such series may be surrendered for registration of transfer or exchange, and where notices and demands to us in respect of the debt securities may be delivered;

• the period or periods within which, the price or prices at which and the terms and conditions upon which we may redeem the debt securities;

• any obligation we have to redeem or purchase the debt securities pursuant to any sinking fund or analogous provisions or at the option of a holder of debt securities and the period or periods within which, the price or prices at which and in the terms and conditions upon which securities of the series shall be redeemed or purchased, in whole or in part, pursuant to such obligation;

• the dates on which and the price or prices at which we will repurchase debt securities at the option of the holders of debt securities and other detailed terms and provisions of these repurchase obligations;

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• the denominations in which the debt securities will be issued, if other than denominations of $1,000 and any integral multiple thereof;

• whether the debt securities will be issued in the form of certificated debt securities or global debt securities;

• the portion of principal amount of the debt securities payable upon declaration of acceleration of the maturity date, if other than the principal amount;

• the currency of denomination of the debt securities, which may be United States Dollars or any foreign currency, and if such currency of denomination is a composite currency, the agency or organization, if any, responsible for overseeing such composite currency;

• the designation of the currency, currencies or currency units in which payment of principal of, premium and interest on the debt securities will be made;

• if payments of principal of, premium or interest on the debt securities will be made in one or more currencies or currency units other than that or those in which the debt securities are denominated, the manner in which the exchange rate with respect to these payments will be determined;

• the manner in which the amounts of payment of principal of, premium, if any, or interest on the debt securities will be determined, if these amounts may be determined by reference to an index based on a currency or currencies or by reference to a commodity, commodity index, stock exchange index or financial index;

• any provisions relating to any security provided for the debt securities;

• any addition to, deletion of or change in the Events of Default described in this prospectus or in the indenture with respect to the debt securities and any change in the acceleration provisions described in this prospectus or in the indenture with respect to the debt securities;

• any addition to, deletion of or change in the covenants described in this prospectus or in the indenture with respect to the debt securities;

• any depositaries, interest rate calculation agents, exchange rate calculation agents or other agents with respect to the debt securities;

• the provisions, if any, relating to conversion or exchange of any debt securities of such series, including if applicable, the conversion or exchange price and period, provisions as to whether conversion or exchange will be mandatory, the events requiring an adjustment of the conversion or exchange price and provisions affecting conversion or exchange;

• any other terms of the debt securities, which may supplement, modify or delete any provision of the indenture as it applies to that series, including any terms that may be required under applicable law or regulations or advisable in connection with the marketing of the securities; and

• whether any of our direct or indirect subsidiaries will guarantee the debt securities of that series, including the terms of subordination, if any, of such guarantees. (Section 2.2)

We may issue debt securities that provide for an amount less than their stated principal amount to be due and payable upon declaration of acceleration of their maturity pursuant to the terms of the indenture. We will provide you with information on the federal income tax considerations and other special considerations applicable to any of these debt securities in the applicable prospectus supplement.

If we denominate the purchase price of any of the debt securities in a foreign currency or currencies or a foreign currency unit or units, or if the principal of and any premium and interest on any series of debt securities is payable in a foreign currency or currencies or a foreign currency unit or units, we will provide you with information on the restrictions, elections, general tax considerations, specific terms and other information with respect to that issue of debt securities and such foreign currency or currencies or foreign currency unit or units in the applicable prospectus supplement.

Transfer and Exchange

Each debt security will be represented by either one or more global securities registered in the name of The Depository Trust Company, or the Depositary, or a nominee of the Depositary (we will refer to any debt security represented by a global debt security as a “book-entry debt security”), or a certificate issued in definitive registered form (we will refer to any debt security represented by a certificated security as a “certificated debt security”) as

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set forth in the applicable prospectus supplement. Except as set forth under the heading “Global Debt Securities and Book-Entry System” below, book-entry debt securities will not be issuable in certificated form.

Certificated Debt Securities. You may transfer or exchange certificated debt securities at any office we maintain for this purpose in accordance with the terms of the indenture. (Section 2.4) No service charge will be made for any transfer or exchange of certificated debt securities, but we may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection with a transfer or exchange. (Section 2.7)

You may effect the transfer of certificated debt securities and the right to receive the principal of, premium and interest on certificated debt securities only by surrendering the certificate representing those certificated debt securities and either reissuance by us or the trustee of the certificate to the new holder or the issuance by us or the trustee of a new certificate to the new holder.

Global Debt Securities and Book-Entry System. Each global debt security representing book-entry debt securities will be deposited with, or on behalf of, the Depositary, and registered in the name of the Depositary or a nominee of the Depositary. Please see “Global Securities.”

Covenants

We will set forth in the applicable prospectus supplement any restrictive covenants applicable to any issue of debt securities. (Article IV).

No Protection in the Event of a Change of Control

Unless we state otherwise in the applicable prospectus supplement, the debt securities will not contain any provisions which may afford holders of the debt securities protection in the event we have a change in control or in the event of a highly leveraged transaction (whether or not such transaction results in a change in control) which could adversely affect holders of debt securities.

Consolidation, Merger and Sale of Assets

We may not consolidate with or merge with or into, or convey, transfer or lease all or substantially all of our properties and assets to any person (a “successor person”) unless:

• we are the surviving entity or the successor person (if other than atai) is a corporation, partnership, trust or other entity organized and validly existing under the laws of the Netherlands and expressly assumes our obligations on the debt securities and under the indenture; and

• immediately after giving effect to the transaction, no Default or Event of Default shall have occurred and be continuing.

Notwithstanding the above, any of our subsidiaries may consolidate with, merge into or transfer all or part of its properties to us. (Section 5.1)

Events of Default

“Event of Default” means with respect to any series of debt securities, any of the following:

• default in the payment of any interest upon any debt security of that series when it becomes due and payable, and continuance of such default for a period of 30 days (unless the entire amount of the payment is deposited by us with the trustee or with a paying agent prior to the expiration of the 30-day period);

• default in the payment of principal of any security of that series at its maturity;

• default in the performance or breach of any other covenant or warranty by us in the indenture (other than a covenant or warranty that has been included in the indenture solely for the benefit of a series of debt securities other than that series), which default continues uncured for a period of 60 days after we receive written notice from the trustee or atai and the trustee receive written notice from the holders of not less than 25% in principal amount of the outstanding debt securities of that series as provided in the indenture;

• certain voluntary or involuntary events of bankruptcy, insolvency or reorganization of atai; or

• any other Event of Default provided with respect to debt securities of that series that is described in the applicable prospectus supplement. (Section 6.1)

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No Event of Default with respect to a particular series of debt securities (except as to certain events of bankruptcy, insolvency or reorganization) necessarily constitutes an Event of Default with respect to any other series of debt securities. (Section 6.1) The occurrence of certain Events of Default or an acceleration under the indenture may constitute an event of default under certain indebtedness of ours or our subsidiaries outstanding from time to time.

We will provide the trustee written notice of any Default or Event of Default within 30 days of becoming aware of the occurrence of such Default or Event of Default, which notice will describe in reasonable detail the status of such Default or Event of Default and what action we are taking or propose to take in respect thereof. (Section 6.1)

If an Event of Default with respect to debt securities of any series at the time outstanding occurs and is continuing, then the trustee or the holders of not less than 25% in principal amount of the outstanding debt securities of that series may, by a notice in writing to us (and to the trustee if given by the holders), declare to be due and payable immediately the principal of (or, if the debt securities of that series are discount securities, that portion of the principal amount as may be specified in the terms of that series) and accrued and unpaid interest, if any, on all debt securities of that series. In the case of an Event of Default resulting from certain events of bankruptcy, insolvency or reorganization, the principal (or such specified amount) of and accrued and unpaid interest, if any, on all outstanding debt securities will become and be immediately due and payable without any declaration or other act on the part of the trustee or any holder of outstanding debt securities. At any time after a declaration of acceleration with respect to debt securities of any series has been made, but before a judgment or decree for payment of the money due has been obtained by the trustee, the holders of a majority in principal amount of the outstanding debt securities of that series may rescind and annul the acceleration if all Events of Default, other than the non-payment of accelerated principal and interest, if any, with respect to debt securities of that series, have been cured or waived as provided in the indenture. (Section 6.2) We refer you to the prospectus supplement relating to any series of debt securities that are discount securities for the particular provisions relating to acceleration of a portion of the principal amount of such discount securities upon the occurrence of an Event of Default.

The indenture will provide that the trustee may refuse to perform any duty or exercise any of its rights or powers under the indenture unless the trustee receives indemnity satisfactory to it against any cost, liability or expense which might be incurred by it in performing such duty or exercising such right or power. (Section 7.1(e)) Subject to certain rights of the trustee, the holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the debt securities of that series. (Section 6.12)

No holder of any debt security of any series will have any right to institute any proceeding, judicial or otherwise, with respect to the indenture or for the appointment of a receiver or trustee, or for any remedy under the indenture, unless:

• that holder has previously given to the trustee written notice of a continuing Event of Default with respect to debt securities of that series; and

• the holders of not less than 25% in principal amount of the outstanding debt securities of that series have made written request, and offered indemnity or security satisfactory to the trustee, to the trustee to institute the proceeding as trustee, and the trustee has not received from the holders of not less than a majority in principal amount of the outstanding debt securities of that series a direction inconsistent with that request and has failed to institute the proceeding within 60 days. (Section 6.7)

Notwithstanding any other provision in the indenture, the holder of any debt security will have an absolute and unconditional right to receive payment of the principal of, premium and any interest on that debt security on or after the due dates expressed in that debt security and to institute suit for the enforcement of payment. (Section 6.8)

The indenture will require us, within 120 days after the end of our fiscal year, to furnish to the trustee a statement as to compliance with the indenture. (Section 4.3) If a Default or Event of Default occurs and is continuing with respect to the securities of any series and if it is known to a responsible officer of the trustee, the trustee shall mail to each securityholder of the securities of that series notice of a Default or Event of Default within 90 days after it occurs or, if later, after a responsible officer of the trustee has knowledge of such Default or Event of Default. The

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indenture will provide that the trustee may withhold notice to the holders of debt securities of any series of any Default or Event of Default (except in payment on any debt securities of that series) with respect to debt securities of that series if the trustee determines in good faith that withholding notice is in the interest of the holders of those debt securities. (Section 7.5)

Modification and Waiver

We and the trustee may modify, amend or supplement the indenture or the debt securities of any series without the consent of any holder of any debt security:

• to cure any ambiguity, defect or inconsistency;

• to comply with covenants in the indenture described above under the heading “Consolidation, Merger and Sale of Assets”;

• to provide for uncertificated securities in addition to or in place of certificated securities;

• to add guarantees with respect to debt securities of any series or secure debt securities of any series;

• to surrender any of our rights or powers under the indenture;

• to add covenants or events of default for the benefit of the holders of debt securities of any series;

• to comply with the applicable procedures of the applicable depositary;

• to make any change that does not adversely affect the rights of any holder of debt securities;

• to provide for the issuance of and establish the form and terms and conditions of debt securities of any series as permitted by the indenture;

• to effect the appointment of a successor trustee with respect to the debt securities of any series and to add to or change any of the provisions of the indenture to provide for or facilitate administration by more than one trustee; or

• to comply with requirements of the SEC in order to effect or maintain the qualification of the indenture under the Trust Indenture Act. (Section 9.1)

We may also modify and amend the indenture with the consent of the holders of at least a majority in principal amount of the outstanding debt securities of each series affected by the modifications or amendments. We may not make any modification or amendment without the consent of the holders of each affected debt security then outstanding if that amendment will:

• reduce the principal amount of debt securities whose holders must consent to an amendment, supplement or waiver;

• reduce the rate of or extend the time for payment of interest (including default interest) on any debt security;

• reduce the principal of or premium on or change the fixed maturity of any debt security or reduce the amount of, or postpone the date fixed for, the payment of any sinking fund or analogous obligation with respect to any series of debt securities;

• reduce the principal amount of discount securities payable upon acceleration of maturity;

• waive a default in the payment of the principal of, premium or interest on any debt security (except a rescission of acceleration of the debt securities of any series by the holders of at least a majority in aggregate principal amount of the then outstanding debt securities of that series and a waiver of the payment default that resulted from such acceleration);

• make the principal of or premium or interest on any debt security payable in currency other than that stated in the debt security;

• make any change to certain provisions of the indenture relating to, among other things, the right of holders of debt securities to receive payment of the principal of, premium and interest on those debt securities and to institute suit for the enforcement of any such payment and to waivers or amendments; or

• waive a redemption payment with respect to any debt security, provided that such redemption is made at our option. (Section 9.3)

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Except for certain specified provisions, the holders of at least a majority in principal amount of the outstanding debt securities of any series may on behalf of the holders of all debt securities of that series waive our compliance with provisions of the indenture. (Section 9.2) The holders of a majority in principal amount of the outstanding debt securities of any series may on behalf of the holders of all the debt securities of such series waive any past default under the indenture with respect to that series and its consequences, except a default in the payment of the principal of, premium or any interest on any debt security of that series; provided, however, that the holders of a majority in principal amount of the outstanding debt securities of any series may rescind an acceleration and its consequences, including any related payment default that resulted from the acceleration. (Section 6.13)

Defeasance of Debt Securities and Certain Covenants in Certain Circumstances

Legal Defeasance. The indenture will provide that, unless otherwise provided by the terms of the applicable series of debt securities, we may be discharged from any and all obligations in respect of the debt securities of any series (subject to certain exceptions). We will be so discharged upon the irrevocable deposit with the trustee, in trust, of money and/or U.S. government obligations or, in the case of debt securities denominated in a single currency other than U.S. Dollars, government obligations of the government that issued or caused to be issued such currency, that, through the payment of interest and principal in accordance with their terms, will provide money or U.S. government obligations in an amount sufficient in the opinion of a nationally recognized firm of independent public accountants or investment bank to pay and discharge each installment of principal, premium and interest on and any mandatory sinking fund payments in respect of the debt securities of that series on the stated maturity of those payments in accordance with the terms of the indenture and those debt securities.

This discharge may occur only if, among other things, we have delivered to the trustee an opinion of counsel stating that we have received from, or there has been published by, the United States Internal Revenue Service a ruling or, since the date of execution of the indenture, there has been a change in the applicable United States federal income tax law, in either case to the effect that, and based thereon such opinion shall confirm that, the holders of the debt securities of that series will not recognize income, gain or loss for United States federal income tax purposes as a result of the deposit, defeasance and discharge and will be subject to United States federal income tax on the same amounts and in the same manner and at the same times as would have been the case if the deposit, defeasance and discharge had not occurred. (Section 8.3)

Defeasance of Certain Covenants. The indenture will provide that, unless otherwise provided by the terms of the applicable series of debt securities, upon compliance with certain conditions:

• we may omit to comply with the covenant described under the heading “Consolidation, Merger and Sale of Assets” and certain other covenants set forth in the indenture, as well as any additional covenants which may be set forth in the applicable prospectus supplement; and

• any omission to comply with those covenants will not constitute a Default or an Event of Default with respect to the debt securities of that series (“covenant defeasance”).

The conditions include:

• depositing with the trustee money and/or U.S. government obligations or, in the case of debt securities denominated in a single currency other than U.S. Dollars, government obligations of the government that issued or caused to be issued such currency, that, through the payment of interest and principal in accordance with their terms, will provide money in an amount sufficient in the opinion of a nationally recognized firm of independent public accountants or investment bank to pay and discharge each installment of principal of, premium and interest on and any mandatory sinking fund payments in respect of the debt securities of that series on the stated maturity of those payments in accordance with the terms of the indenture and those debt securities; and

• delivering to the trustee an opinion of counsel to the effect that the holders of the debt securities of that series will not recognize income, gain or loss for United States federal income tax purposes as a result of the deposit and related covenant defeasance and will be subject to United States federal income tax on the same amounts and in the same manner and at the same times as would have been the case if the deposit and related covenant defeasance had not occurred. (Section 8.4)

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No Personal Liability of Directors, Officers, Employees or Securityholders

None of our past, present or future directors, officers, employees or securityholders, as such, will have any liability for any of our obligations under the debt securities or the indenture or for any claim based on, or in respect or by reason of, such obligations or their creation. By accepting a debt security, each holder waives and releases all such liability. This waiver and release is part of the consideration for the issue of the debt securities. However, this waiver and release may not be effective to waive liabilities under U.S. federal securities laws, and it is the view of the SEC that such a waiver is against public policy.

Governing Law

The indenture and the debt securities, including any claim or controversy arising out of or relating to the indenture or the securities, will be governed by the laws of the State of New York.

The indenture will provide that we, the trustee and the holders of the debt securities (by their acceptance of the debt securities) irrevocably waive, to the fullest extent permitted by applicable law, any and all right to trial by jury in any legal proceeding arising out of or relating to the indenture, the debt securities or the transactions contemplated thereby.

The indenture will provide that any legal suit, action or proceeding arising out of or based upon the indenture or the transactions contemplated thereby may be instituted in the federal courts of the United States of America located in the City of New York or the courts of the State of New York in each case located in the City of New York, and we, the trustee and the holder of the debt securities (by their acceptance of the debt securities) irrevocably submit to the non-exclusive jurisdiction of such courts in any such suit, action or proceeding. The indenture will further provide that service of any process, summons, notice or document by mail (to the extent allowed under any applicable statute or rule of court) to such party’s address set forth in the indenture will be effective service of process for any suit, action or other proceeding brought in any such court. The indenture will further provide that we, the trustee and the holders of the debt securities (by their acceptance of the debt securities) irrevocably and unconditionally waive any objection to the laying of venue of any suit, action or other proceeding in the courts specified above and irrevocably and unconditionally waive and agree not to plead or claim any such suit, action or other proceeding has been brought in an inconvenient forum. (Section 10.10)

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DESCRIPTION OF WARRANTS

We may issue warrants for the purchase of our common shares or of debt securities. We may issue warrants independently or together with other securities, and the warrants may be attached to or separate from any offered securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and the investors or a warrant agent.

The following summary of material provisions of the warrants and warrant agreements are subject to, and qualified in their entirety by reference to, all the provisions of the warrant agreement and warrant certificate applicable to a particular series of warrants. The terms of any warrants offered under a prospectus supplement may differ from the terms described below. We urge you to read the applicable prospectus supplement and any related free writing prospectus, as well as the complete warrant agreements and warrant certificates that contain the terms of the warrants.

The particular terms of any issue of warrants will be described in the prospectus supplement relating to the issue. Those terms may include:

• the number of common shares purchasable upon the exercise of warrants to purchase such shares and the price at which such number of common shares may be purchased upon such exercise;

• the principal amount of debt securities that may be purchased upon exercise of a debt warrant and the exercise price for the warrants, which may be payable in cash, securities or other property;

• the date, if any, on and after which the warrants and the related debt securities or common shares will be separately transferable;

• the terms of any rights to redeem or call the warrants;

• the date on which the right to exercise the warrants will commence and the date on which the right will expire;

• United States Federal income tax consequences applicable to the warrants; and

• any additional terms of the warrants, including terms, procedures, and limitations relating to the exchange, exercise and settlement of the warrants.

Holders of warrants to purchase common shares will not be entitled:

• to vote, consent or receive dividends, if any, or payments upon our liquidation or dissolution;

• receive notice as shareholders with respect to any general meeting for the appointment of our directors or any other matter; or

• exercise any rights as shareholders of atai.

Each warrant will entitle its holder to purchase the principal amount of debt securities or the number of common shares at the exercise price set forth in, or calculable as set forth in, the applicable prospectus supplement. Unless we otherwise specify in the applicable prospectus supplement, holders of the warrants may exercise the warrants at any time up to the specified time on the expiration date that we set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

A holder of warrant certificates may exchange them for new warrant certificates of different denominations, present them for registration of transfer and exercise them at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement. Until any warrants to purchase debt securities are exercised, the holder of the warrants will not have any rights of holders of the debt securities that can be purchased upon exercise, including any rights to receive payments of principal, premium or interest on the underlying debt securities or to enforce covenants in the applicable indenture. Until any warrants to purchase common shares are exercised, the holders of the warrants will not have any rights of holders of the underlying common shares, including any rights to receive dividends or payments upon any liquidation or dissolution on the common shares, if any.

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DESCRIPTION OF UNITS

We may issue units consisting of any combination of the other types of securities offered under this prospectus in one or more series. We may evidence each series of units by unit certificates that we will issue under a separate agreement. We may enter into unit agreements with a unit agent. Each unit agent will be a bank or trust company that we select. We will indicate the name and address of the unit agent in the applicable prospectus supplement relating to a particular series of units.

The following description, together with the additional information included in any applicable prospectus supplement, summarizes the general features of the units that we may offer under this prospectus. You should read any prospectus supplement and any free writing prospectus that we may authorize to be provided to you related to the series of units being offered, as well as the complete unit agreements that contain the terms of the units. Specific unit agreements will contain additional important terms and provisions and we will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from another report that we file with the SEC, the form of each unit agreement relating to units offered under this prospectus.

If we offer any units, certain terms of that series of units will be described in the applicable prospectus supplement, including, without limitation, the following, as applicable:

• the title of the series of units;

• identification and description of the separate constituent securities comprising the units;

• the price or prices at which the units will be issued;

• the date, if any, on and after which the constituent securities comprising the units will be separately transferable;

• a discussion of certain United States federal income tax considerations applicable to the units; and

• any other terms of the units and their constituent securities.

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GLOBAL SECURITIES

Book-Entry, Delivery and Form

Unless we indicate differently in any applicable prospectus supplement or free writing prospectus, the securities initially will be issued in book-entry form and represented by one or more global notes or global securities, or, collectively, global securities. These global securities, to the extent issued for our common shares, shall be share certificates (aandeelbewijzen) for registered shares under Dutch law, in accordance with our articles of association. The global securities will be deposited with, or on behalf of, The Depository Trust Company, New York, New York, as depositary, or DTC, and registered in the name of Cede & Co., the nominee of DTC. Unless and until it is exchanged for individual certificates (such individual certificates, to the extent issued for our common shares, being share certificates (aandeelbewijzen) under Dutch law, in accordance with our articles of association) evidencing securities under the limited circumstances described below, a global security may not be transferred except as a whole by the depositary to its nominee or by the nominee to the depositary, or by the depositary or its nominee to a successor depositary or to a nominee of the successor depositary.

DTC has advised us that it is:

• a limited-purpose trust company organized under the New York Banking Law;

• a “banking organization” within the meaning of the New York Banking Law;

• a member of the Federal Reserve System;

• a “clearing corporation” within the meaning of the New York Uniform Commercial Code; and

• a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act.

DTC holds securities that its participants deposit with DTC. DTC also facilitates the settlement among its participants of securities transactions, such as transfers and pledges, in deposited securities through electronic computerized book-entry changes in participants’ accounts, thereby eliminating the need for physical movement of securities certificates. “Direct participants” in DTC include securities brokers and dealers, including underwriters, banks, trust companies, clearing corporations and other organizations. DTC is a wholly-owned subsidiary of The Depository Trust & Clearing Corporation, or DTCC. DTCC is the holding company for DTC, National Securities Clearing Corporation and Fixed Income Clearing Corporation, all of which are registered clearing agencies. DTCC is owned by the users of its regulated subsidiaries. Access to the DTC system is also available to others, which we sometimes refer to as indirect participants, that clear through or maintain a custodial relationship with a direct participant, either directly or indirectly. The rules applicable to DTC and its participants are on file with the SEC.

Purchases of securities under the DTC system must be made by or through direct participants, which will receive a credit for the securities on DTC’s records. The ownership interest of the actual purchaser of a security, which we sometimes refer to as a beneficial owner, is in turn recorded on the direct and indirect participants’ records. Beneficial owners of securities will not receive written confirmation from DTC of their purchases. However, beneficial owners are expected to receive written confirmations providing details of their transactions, as well as periodic statements of their holdings, from the direct or indirect participants through which they purchased securities. Transfers of ownership interests in global securities are to be accomplished by entries made on the books of participants acting on behalf of beneficial owners. Beneficial owners will not receive certificates representing their ownership interests in the global securities, except under the limited circumstances described below.

To facilitate subsequent transfers, all global securities deposited by direct participants with DTC will be registered in the name of DTC’s partnership nominee, Cede & Co., or such other name as may be requested by an authorized representative of DTC. The deposit of securities with DTC and their registration in the name of Cede & Co. or such other nominee will not change the beneficial ownership of the securities. DTC has no knowledge of the actual beneficial owners of the securities. DTC’s records reflect only the identity of the direct participants to whose accounts the securities are credited, which may or may not be the beneficial owners. The participants are responsible for keeping account of their holdings on behalf of their customers.

So long as the securities are in book-entry form, you will receive payments and may transfer securities only through the facilities of the depositary and its direct and indirect participants. We will maintain an office or agency in the location specified in the prospectus supplement for the applicable securities, where notices and demands in respect of the securities and the indenture may be delivered to us and where certificated securities may be surrendered for payment, registration of transfer or exchange.

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Conveyance of notices and other communications by DTC to direct participants, by direct participants to indirect participants and by direct participants and indirect participants to beneficial owners will be governed by arrangements among them, subject to any legal requirements in effect from time to time.

Redemption notices will be sent to DTC. If less than all of the securities of a particular series are being redeemed, DTC’s practice is to determine by lot the amount of the interest of each direct participant in the securities of such series to be redeemed.

Neither DTC nor Cede & Co. (or such other DTC nominee) will consent or vote with respect to the securities. Under its usual procedures, DTC will mail an omnibus proxy to us as soon as possible after the record date. The omnibus proxy assigns the consenting or voting rights of Cede & Co. to those direct participants to whose accounts the securities of such series are credited on the record date, identified in a listing attached to the omnibus proxy.

So long as securities are in book-entry form, we will make payments on those securities to the depositary or its nominee, as the registered owner of such securities, by wire transfer of immediately available funds. If securities are issued in definitive certificated form under the limited circumstances described below and unless if otherwise provided in the description of the applicable securities herein or in the applicable prospectus supplement, we will have the option of making payments by check mailed to the addresses of the persons entitled to payment or by wire transfer to bank accounts in the United States designated in writing to the applicable trustee or other designated party at least 15 days before the applicable payment date by the persons entitled to payment, unless a shorter period is satisfactory to the applicable trustee or other designated party.

Redemption proceeds, distributions and dividend payments on the securities will be made to Cede & Co., or such other nominee as may be requested by an authorized representative of DTC. DTC’s practice is to credit direct participants’ accounts upon DTC’s receipt of funds and corresponding detail information from us on the payment date in accordance with their respective holdings shown on DTC records. Payments by participants to beneficial owners will be governed by standing instructions and customary practices, as is the case with securities held for the account of customers in bearer form or registered in “street name.” Those payments will be the responsibility of participants and not of DTC or us, subject to any statutory or regulatory requirements in effect from time to time. Payment of redemption proceeds, distributions and dividend payments to Cede & Co., or such other nominee as may be requested by an authorized representative of DTC, is our responsibility, disbursement of payments to direct participants is the responsibility of DTC, and disbursement of payments to the beneficial owners is the responsibility of direct and indirect participants.

Except under the limited circumstances described below, purchasers of securities will not be entitled to have securities registered in their names and will not receive physical delivery of securities. Accordingly, each beneficial owner must rely on the procedures of DTC and its participants to exercise any rights under the securities and the indenture.

The laws of some jurisdictions may require that some purchasers of securities take physical delivery of securities in definitive form. Those laws may impair the ability to transfer or pledge beneficial interests in securities.

DTC may discontinue providing its services as securities depositary with respect to the securities at any time by giving reasonable notice to us. Under such circumstances, in the event that a successor depositary is not obtained, securities certificates are required to be printed and delivered.

As noted above, beneficial owners of a particular series of securities generally will not receive certificates representing their ownership interests in those securities. However, if:

• DTC notifies us that it is unwilling or unable to continue as a depositary for the global security or securities representing such series of securities or if DTC ceases to be a clearing agency registered under the Exchange Act at a time when it is required to be registered and a successor depositary is not appointed within 90 days of the notification to us or of our becoming aware of DTC’s ceasing to be so registered, as the case may be;

• we determine, in our sole discretion, not to have such securities represented by one or more global securities; or

• an Event of Default has occurred and is continuing with respect to such series of securities,

we will prepare and deliver certificates for such securities in exchange for beneficial interests in the global securities. Any beneficial interest in a global security that is exchangeable under the circumstances described in the preceding sentence will be exchangeable for securities in definitive certificated form registered in the names that the depositary directs. It is expected that these directions will be based upon directions received by the depositary from its participants with respect to ownership of beneficial interests in the global securities.

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Euroclear and Clearstream

If so provided in the applicable prospectus supplement, you may hold interests in a global security through Clearstream Banking S.A., which we refer to as “Clearstream,” or Euroclear Bank S.A./N.V., as operator of the Euroclear System, which we refer to as “Euroclear,” either directly if you are a participant in Clearstream or Euroclear or indirectly through organizations which are participants in Clearstream or Euroclear. Clearstream and Euroclear will hold interests on behalf of their respective participants through customers’ securities accounts in the names of Clearstream and Euroclear, respectively, on the books of their respective U.S. depositaries, which in turn will hold such interests in customers’ securities accounts in such depositaries’ names on DTC’s books.

Clearstream and Euroclear are securities clearance systems in Europe. Clearstream and Euroclear hold securities for their respective participating organizations and facilitate the clearance and settlement of securities transactions between those participants through electronic book-entry changes in their accounts, thereby eliminating the need for physical movement of certificates.

Payments, deliveries, transfers, exchanges, notices and other matters relating to beneficial interests in global securities owned through Euroclear or Clearstream must comply with the rules and procedures of those systems. Transactions between participants in Euroclear or Clearstream, on one hand, and other participants in DTC, on the other hand, are also subject to DTC’s rules and procedures.

Investors will be able to make and receive through Euroclear and Clearstream payments, deliveries, transfers and other transactions involving any beneficial interests in global securities held through those systems only on days when those systems are open for business. Those systems may not be open for business on days when banks, brokers and other institutions are open for business in the United States.

Cross-market transfers between participants in DTC, on the one hand, and participants in Euroclear or Clearstream, on the other hand, will be effected through DTC in accordance with the DTC’s rules on behalf of Euroclear or Clearstream, as the case may be, by their respective U.S. depositaries; however, such cross-market transactions will require delivery of instructions to Euroclear or Clearstream, as the case may be, by the counterparty in such system in accordance with the rules and procedures and within the established deadlines (European time) of such system. Euroclear or Clearstream, as the case may be, will, if the transaction meets its settlement requirements, deliver instructions to its U.S. depositary to take action to effect final settlement on its behalf by delivering or receiving interests in the global securities through DTC, and making or receiving payment in accordance with normal procedures for same-day fund settlement. Participants in Euroclear or Clearstream may not deliver instructions directly to their respective U.S. depositaries.

Due to time zone differences, the securities accounts of a participant in Euroclear or Clearstream purchasing an interest in a global security from a direct participant in DTC will be credited, and any such crediting will be reported to the relevant participant in Euroclear or Clearstream, during the securities settlement processing day (which must be a business day for Euroclear or Clearstream) immediately following the settlement date of DTC. Cash received in Euroclear or Clearstream as a result of sales of interests in a global security by or through a participant in Euroclear or Clearstream to a direct participant in DTC will be received with value on the settlement date of DTC but will be available in the relevant Euroclear or Clearstream cash account only as of the business day for Euroclear or Clearstream following DTC’s settlement date.

Other

The information in this section of this prospectus concerning DTC, Clearstream, Euroclear and their respective book-entry systems has been obtained from sources that we believe to be reliable, but we do not take responsibility for this information. This information has been provided solely as a matter of convenience. The rules and procedures of DTC, Clearstream and Euroclear are solely within the control of those organizations and could change at any time. Neither we nor the trustee nor any agent of ours or of the trustee has any control over those entities and none of us takes any responsibility for their activities. You are urged to contact DTC, Clearstream and Euroclear or their respective participants directly to discuss those matters. In addition, although we expect that DTC, Clearstream and Euroclear will perform the foregoing procedures, none of them is under any obligation to perform or continue to perform such procedures and such procedures may be discontinued at any time. Neither we nor any agent of ours will have any responsibility for the performance or nonperformance by DTC, Clearstream and Euroclear or their respective participants of these or any other rules or procedures governing their respective operations.

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SELLING SECURITYHOLDERS

Information about additional selling securityholders, where applicable, may be set forth in a prospectus supplement, in a post-effective amendment or in filings we make with the SEC under the Exchange Act that are incorporated by reference. The selling securityholders identified in the table below may, from time to time, offer and sell up to 45,321,301 common shares offered by this prospectus and any accompanying prospectus supplement. In the event such selling securityholders or any other selling securityholders acquire additional common shares, including, but not limited to, additional securities convertible, exchangeable or exercisable into additional common shares, information about these selling securityholders, where applicable, may be set forth in a prospectus supplement, in a post-effective amendment or in filings we make with the SEC under the Exchange Act that are incorporated by reference. When we refer to the selling securityholders identified in the table below, we mean the entities identified in the table, and the donees, pledgees, transferees, assignees, designees, distributees or other successors-in-interest who after the date of this prospectus come to hold any of such selling securityholders’ respective interests in our common shares other than through a public sale.

The possible resale of our common shares by the selling securityholders identified in the table below relates to (i) 6,185,904 common shares issued or issuable upon the conversion of 386,619 convertible notes that we originally issued between November 2018 and October 2020 to certain of the selling securityholders identified below, (ii) 9,993,341 common shares purchased by certain of the selling securityholders (the “Initial PIPE Investors”) identified below pursuant to subscription agreements, dated June 2, 2025 (the “Initial Subscription Agreements”), (iii) 6,311,006 common shares issuable upon the exercise of a pre-funded warrant issued to one of the Initial PIPE Investors pursuant to one of the Initial Subscription Agreements, (iv) 18,264,840 common shares purchased by certain of the selling securityholders (the “Subsequent PIPE Investors”) identified below pursuant to subscription agreements, dated July 1, 2025 (the “Subsequent Subscription Agreements”) and (v) 4,566,210 common shares issuable upon the exercise of a pre-funded warrant issued to one of the Subsequent PIPE Investors pursuant to one of the Subsequent Subscription Agreements. In connection with entering into the Initial Subscription Agreements and the Subsequent Subscription Agreements, we entered into registration rights agreements, dated June, 2, 2025, and July 1, 2025, respectively, with the Initial PIPE Investors and Subsequent PIPE Investors, as applicable, pursuant to which we granted certain registration rights with respect to the securities purchased by the Initial PIPE Investors and Subsequent PIPE Investors, as applicable, and we are registering certain of the securities offered by this prospectus on their behalf.

The following table sets forth information as September 15, 2025, regarding the beneficial ownership of our common shares held by the selling security holders identified below, and the number of our common shares that may from time to time be offered or sold by the selling securityholders pursuant to this prospectus. We have prepared the following table based on information given to us by, or on behalf of, the selling securityholders identified below on or before the date hereof with respect to the beneficial ownership of our common shares held by such selling securityholders.

We have not independently verified this information, and this information may change from time to time and any changed information will be set forth in supplements to this prospectus or in a post-effective amendment, if and when necessary. The selling securityholders identified below may offer all, some or none of their common shares, and we cannot advise you as to whether they will in fact sell any or all of such common shares. In addition, the selling securityholders identified below may have sold, transferred or otherwise disposed of, or may sell, transfer or otherwise dispose of, at any time and from time to time, our common shares in transactions exempt from the registration requirements of the Securities Act after the date on which they provided the information set forth in the table below.

The number of common shares beneficially owned by each selling securityholder is determined in accordance with the rules of the SEC, and the information is not necessarily indicative of beneficial ownership for any other purpose. Under such rules, beneficial ownership includes any common shares over which the individual or entity has sole or shared voting power or investment power. Applicable percentage ownership is based on 233,779,400 common shares outstanding as of September 15, 2025. In computing the number of common shares beneficially owned by an individual or entity and the percentage ownership of that person, common shares subject to options, restricted share units or other rights held by such person that are currently exercisable or will become exercisable or will vest within 60 days of September 15, 2025 are considered outstanding, although these common shares are not considered outstanding for purposes of computing the percentage ownership of any other person. Except as otherwise indicated, and subject to applicable community property laws, the persons identified in the table have sole voting and investment power with respect to all common shares held by that person. The information regarding common shares beneficially owned after the offering assumes the sale of all common shares offered by the selling securityholders

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identified below, and that such selling securityholders do not acquire any additional common shares or additional securities convertible, exchangeable or exercisable into additional common shares. Information in the table below is based on information filed with the SEC or obtained from the persons identified below.

Unless otherwise indicated below, the address for each beneficial owner is ATAI Life Sciences N.V., Prof. J.H. Bavincklaan 7, 1183 AT Amstelveen, the Netherlands.

			Prior to this Prospectus						Maximum Number of Common Shares Subject to Resale Pursuant to this Prospectus			After Resale of All Common Shares Subject to Resale Pursuant to this Prospectus
Selling Securityholders			Number			%			Number			Number			%
Apeiron Investment Group Ltd.(1)			55,211,716			23.62%			11,042,999(2)			44,168,717			18.70%
Adage Capital Partners LP(3)			5,434,782			2.32%			5,434,782			—			—
ADAR1 Partners, LP(4)			782,648			0.33%			782,648			—			—
Ally Bridge MedAlpha Master Fund L.P.(5)			2,283,105			0.98%			2,283,105			—			—
Ferring Ventures S.A.(6)			15,503,775			4.99%			15,435,775			68,000			0.03%
Galaxy Group Funding ECI U LLC(7)			913,242			0.39%			913,242			—			—
Hypothalmus Ltd(8)			4,566,210			1.95%			4,566,210			—			—
Seligman Healthcare Spectrum (Master) Fund(9)			913,242			0.39%			913,242			—			—
Spearhead Insurance Solutions IDF, LLC - Series ADAR1(10)			130,594			0.06%			130,594			—			—
Wilde Ventures GmbH(11)			3,818,704			1.63%			3,818,704			—			—

(1)
Based solely on the Schedule 13D/A jointly filed with the SEC on August 18, 2025 by Apeiron Investment Group Ltd. (“Apeiron”), Apeiron Presight Capital Fund II, L.P. (“Presight II”), Presight Capital Management I, L.L.C. (“Presight Management”), Fabien Hansen and Christian Angermayer. As of August 14, 2025, Apeiron and Mr. Angermayer reported shared voting and dispositive power over 55,211,716 common shares, and Presight II and Fabian Hansen reported shared voting and dispositive power over 1,799,302 common shares. Presight II is the record holder of 1,799,302 common shares. Apeiron and Mr. Hansen are the managing members of Presight Management, which is the general partner of Presight II. As a result, each of Apeiron, Mr. Hansen and Presight Management may be deemed to share beneficial ownership of the securities held by Presight II. Apeiron is the record holder of 51,045,214 common shares and may be deemed to own an additional 2,367,200 common shares underlying convertible notes. Mr. Angermayer is the majority shareholder of Apeiron and may be deemed to share beneficial ownership of the securities beneficially owned by Apeiron. The principal business address for Apeiron, and Mr. Angermayer is 66 & 67, Amery Street, SLM1707, Sliema, Malta. The principal business address for Presight II, Presight Management and Mr. Hansen is 440 N Barranca Ave #3391 Covina, California 91723.

(2)
Consists of (i) 8,675,799 common shares acquired pursuant to one of the Subsequent Subscription Agreements and (ii) 2,367,200 shares issuable upon the conversion of 147,950 convertible notes.

(3)
Consists of 5,434,782 common shares held by Adage Capital Partners LP (“Adage”), whose principal offices are located at 200 Clarendon Street, Boston Massachusetts, 02116. Bob Atchinson and Phillip Gross are the managing members of Adage Capital Advisors, L.L.C., which is the managing member of Adage Capital Partners GP, L.L.C., which is the general partner of Adage, and each such person or entity, as the case may be, has shared voting and/or investment power over the securities held by Adage and may be deemed the beneficial owner of such shares, and each such person or entity, as the case may be, disclaims beneficial ownership of such securities except to the extent of their respective pecuniary interest therein.

(4)
Consists of 782,648 common shares held by ADAR1 Partners, LP, whose principal offices are located at 3503 Wild Cherry Drive, Building 9, Austin, Texas 78738.

(5)
Consists of 2,283,105 common shares held by Ally Bridge MedAlpha Master Fund L.P. (“MedAlpha”). Mr. Fan Yu is the sole shareholder of ABG Management Ltd., which is the sole member of Ally Bridge Group (NY) LLC, which manages investments of MedAlpha. As such, each of the foregoing entities and Mr. Fan Yu may be deemed to share beneficial ownership of the shares held by MedAlpha. Each of them disclaims any such beneficial ownership. The address of the above person and entities is 430 Park Avenue, 12th Floor, New York, NY 10022.

(6)
Consists of (i) 4,626,559 common shares, which is inclusive of 4,558,559 common shares acquired pursuant to one of the Initial Subscription Agreements, and (ii) 10,877,216 common shares issuable upon the exercise of pre-funded warrants, which are exercisable subject to a beneficial ownership limitation that provides such warrants may only be exercised to the extent that immediately following such exercise the holder will not beneficially own more than 4.99% of the outstanding common shares. Each of the common shares and pre-funded warrants are held by Ferring Ventures S.A., whose principal offices are located at Chemin de la Vergognausaz 50, 1162 St-Prex, Switzerland.

(7)
Consists of 913,242 common shares held by Galaxy Group Funding ECI U LLC, whose principal offices are located at 107 Grand St, 6th Floor, New York, New York 10013.

(8)
Consists of 4,566,210 common shares held by Hypothalmus Ltd, whose principal offices are located at Binzemühlestrasse 80, CH-8050 Zürich, Switzerland.

(9)
Consists of 913,242 common shares held by Seligman Healthcare Spectrum (Master) Fund, whose principal offices are located at 290 Congress Street, Boston, Massachusetts 02210.

(10)
Consists of 130,594 common shares held by Spearhead Insurance Solutions IDF, LLC - Series ADAR1, whose principal offices are at 3503 Wild Cherry Drive, Building 9, Austin, Texas 78738.

(11)
Consists of 3,818,704 common shares issued upon the conversion on September 11, 2025 of 238,669 convertible notes held by Wilde Ventures GmbH, whose principal offices are located at In der Rehwiese 3, 40629 Düsseldorf, Federal Republic of Germany.

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PLAN OF DISTRIBUTION

We or any of the selling securityholders, including such selling securityholders’ respective donees, pledgees, transferees, assignees, designees, distributees or other successors-in-interest selling our common shares or interests in our common shares received after the date of this prospectus from such selling securityholders as a gift, pledge, partnership distribution or other transfer other than through a public sale, may sell the offered securities from time to time, separately or together, covered by this prospectus. Registration of the securities covered by this prospectus does not mean, however, that those securities necessarily will be offered or sold.

The securities covered by this prospectus may be sold from time to time, at market prices prevailing at the time of sale, at prices related to market prices, at a fixed price or prices subject to change or at negotiated prices, by a variety of methods including, but not limited to, the following:

• on any national securities exchange on which our common shares may be listed at the time of sale, including the Nasdaq Global Market (including through “at-the-market” offerings);

• in the over-the-counter market;

• in privately negotiated transactions;

• through broker-dealers, who may act as agents or principals;

• through one or more underwriters on a firm commitment or best-efforts basis;

• in a block trade in which a broker-dealer may attempt to sell a block of common shares as agent or may position and resell all or a portion of the block as principal to facilitate the transaction;

• through put or call option transactions relating to our common shares;

• through the writing or settlement of options or other hedging transactions, whether through an options exchange or otherwise, and/or the settlement of margin transactions;

• directly to one or more purchasers;

• through agents;

• through loans or pledges of our common shares, including to a broker-dealer or an affiliate thereof; or

• through a combination of any of these methods of sale or by any other legally available means.

In effecting sales, brokers or dealers engaged by us and/or the selling securityholders may arrange for other brokers or dealers to participate. Broker/dealer transactions may include:

• purchases of our common shares by a broker-dealer as principal and resales of our common shares by the broker-dealer for its account pursuant to this prospectus;

• ordinary brokerage transactions; or

• transactions in which the broker/dealer solicits purchasers on a best efforts basis.

At any time a particular offer of the common shares covered by this prospectus is made, a revised prospectus or prospectus supplement, if required, will set forth the aggregate amount of common shares covered by this prospectus being offered and the terms of the offering, including the name or names of any underwriters, dealers, brokers or agents. In addition, to the extent required, any discounts, commissions, concessions and other items constituting underwriters’ or agents’ compensation, as well as any discounts, commissions or concessions allowed or reallowed or paid to dealers, will be set forth in such prospectus supplement. To the extent required, any such prospectus supplement, and, if necessary, a post-effective amendment to the registration statement of which this prospectus is a part, will be filed with the SEC to reflect the disclosure of additional information with respect to the distribution of the common shares covered by this prospectus.

If the selling securityholders utilize a dealer in the sale of the securities being offered pursuant to this prospectus, the selling securityholders will sell the securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale. The selling securityholders may also authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities at the public offering price set forth in the revised prospectus or prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. The conditions to these contracts and

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the commission that the selling securityholders must pay for solicitation of these contracts will be described in a revised prospectus or prospectus supplement, to the extent such revised prospectus or prospectus supplement is required.

The selling securityholders may, from time to time, pledge or grant a security interest in some of the common shares owned by them and, if a selling securityholder defaults in the performance of its secured obligations, the pledgees or secured parties may offer and sell such common shares, as applicable, from time to time, under this prospectus, or under an amendment or supplement to this prospectus. The selling securityholders also may transfer our common shares in other circumstances, in which case the transferees, pledgees or other successors-in-interest will be the selling beneficial owners for purposes of this prospectus.

In connection with the sale of common shares or interests therein, the selling securityholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of our common shares in the course of hedging the positions they assume. The selling securityholders may also sell common shares short and deliver these securities to close out their short positions, or loan or pledge common shares to broker-dealers that in turn may sell these securities. The selling securityholders may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities that require the delivery to such broker-dealer or other financial institution of the common shares offered by this prospectus, which common shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

In connection with the sale of the common shares covered by this prospectus through underwriters, underwriters may receive compensation in the form of underwriting discounts or commissions and may also receive commissions from purchasers of shares of common shares for whom they may act as agent. Underwriters may sell to or through dealers, and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for whom they may act as agent.

Any common shares will be listed on the Nasdaq Global Market, but any other securities may or may not be listed on a national securities exchange. To facilitate the offering of securities, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. This may include over-allotments or short sales of the securities, which involve the sale by persons participating in the offering of more securities than were sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option, if any. In addition, these persons may stabilize or maintain the price of the securities by bidding for or purchasing securities in the open market or by imposing penalty bids, whereby selling concessions allowed to dealers participating in the offering may be reclaimed if securities sold by them are repurchased in connection with stabilization transactions. The effect of these transactions may be to stabilize or maintain the market price of the securities at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

We may engage in at the market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. In addition, we may enter into derivative transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of shares, and may use securities received from us in settlement of those derivatives to close out any related open borrowings of shares. The third party in such sale transactions will be an underwriter and, if not identified in this prospectus, will be named in the applicable prospectus supplement (or a post-effective amendment). In addition, we may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus and an applicable prospectus supplement. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

The specific terms of any lock-up provisions in respect of any given offering will be described in the applicable prospectus supplement.

Any underwriters, broker/dealers or agents participating in the distribution of common shares covered by this prospectus may be deemed to be “underwriters” within the meaning of the Securities Act, and any commissions

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received by any of those underwriters, broker/dealers or agents may be deemed to be underwriting commissions under the Securities Act. A selling securityholder may be deemed to be an “underwriter” within the meaning of the Securities Act with respect to the sale of the common shares covered by this prospectus.

We and the selling securityholders may agree to indemnify underwriters, broker-dealers or agents against certain liabilities, including liabilities under the Securities Act and may also agree to contribute to payments which the underwriters, broker/dealers or agents may be required to make.

Certain of the underwriters, broker/dealers or agents who may become involved in the sale of our common shares may engage in transactions with and perform other services for us in the ordinary course of their business for which they receive customary compensation.

Some of the common shares covered by this prospectus may be sold by selling securityholders in private transactions or under Rule 144 under the Securities Act or another available exemption from the registration requirements of the Securities Act rather than pursuant to this prospectus.

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LEGAL MATTERS

Latham & Watkins LLP will pass upon certain legal matters relating to the issuance and sale of the debt securities, warrants and units. NautaDutilh N.V. will pass upon certain legal matters relating to the issuance of the common shares. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we will name in the applicable prospectus supplement.

EXPERTS

The financial statements of ATAI Life Sciences N.V. as of December 31, 2024 and 2023, and for each of the two years in the period ended December 31, 2024, incorporated by reference in this prospectus, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm given their authority as experts in accounting and auditing.

The audited historical financial statements of Beckley Psytech Limited included in Exhibit 99.1 of ATAI Life Sciences N.V.’s Current Report on Form 8-K, dated September 29, 2025, have been so incorporated in reliance on the report (which contains an explanatory paragraph relating to the Beckley Psytech Limited’s ability to continue as a going concern as described in Note 1 to the financial statements) of PricewaterhouseCoopers LLP, independent auditors, given on the authority of said firm as experts in auditing and accounting.

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23,725,000 Common Shares

PROSPECTUS SUPPLEMENT

Lead Bookrunner

Jefferies

Passive Bookrunner

Berenberg

Co-Managers
Oppenheimer & Co.			Canaccord Genuity

FAQ

What did ATAI (ATAI) announce in this prospectus supplement?

ATAI is offering 23,725,000 common shares at $5.48 per share, a primary equity raise with gross proceeds of $130,013,000.

How much cash will ATAI receive from the offering and what is the use of proceeds?

Proceeds are $121,712,191.90 before expenses and about $121.2 million net. Funds will support clinical development, working capital and general corporate purposes.

Is there an over-allotment option in ATAI’s (ATAI) deal?

Yes. Underwriters may purchase up to 3,558,750 additional shares within 30 days at the public offering price less the underwriting discount.

What will ATAI’s share count be after the offering?

Shares outstanding will be 235,969,597 after the offering, or 239,528,347 if the option is exercised, versus 212,244,597 as of June 30, 2025.

What are ATAI’s preliminary cash and liquidity figures?

ATAI expects approximately $114.6 million in cash, cash equivalents and short‑term investments as of September 30, 2025.

Who are the underwriters and what is the lock-up for ATAI (ATAI)?

Jefferies is lead bookrunner, with Berenberg as passive bookrunner and Oppenheimer & Co. and Canaccord Genuity as co‑managers. ATAI agreed to a 90‑day lock‑up, subject to exceptions.

What recent strategic and regulatory updates are included?

ATAI plans to issue 105,044,902 shares for a Beckley Psytech combination (subject to shareholder approval) and noted FDA Breakthrough Therapy designation for BPL‑003.