[424B5] RAPT Therapeutics, Inc. Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

RAPT Therapeutics (RAPT) launched a primary offering of common stock via a preliminary prospectus supplement under its Form S-3 shelf. The filing includes a 30-day option for underwriters to purchase additional shares at the public offering price, less underwriting discounts and commissions. RAPT’s stock trades on Nasdaq as “RAPT”; the last reported sale price was $33.67 per share on October 20, 2025.

RAPT intends to use net proceeds, together with existing cash, to advance RPT904 in food allergies and chronic spontaneous urticaria (CSU), support other pipeline initiatives, and for working capital and general corporate purposes. Shares outstanding were 16,536,069 as of June 30, 2025.

RAPT and Jeyou reported positive topline Phase 2 CSU data for RPT904, showing numerically greater UAS7 improvements and higher UAS7=0 rates at Weeks 8, 12 and 16 versus omalizumab, with no serious adverse events related to study drug and no treatment-related discontinuations. The companies plan to discuss Phase 3 development with regulators and to initiate a Phase 2b trial in food allergies before the end of 2025.

Insights

Biopharma equity & clinical strategy

Primary stock offering alongside encouraging Phase 2 CSU topline data.

RAPT filed a preliminary supplement for a primary common stock offering under an effective S-3 shelf, with a 30-day underwriters’ option. Proceeds are earmarked to advance RPT904 in food allergy and CSU, plus broader pipeline and general purposes. This is a financing step; ultimate dilution depends on final size and pricing.

Topline results from Jeyou’s Phase 2 CSU study showed numerically greater UAS7 improvements and higher UAS7=0 rates for RPT904 dosed Q8W or Q12W versus omalizumab Q4W across Weeks 8–16, with no serious adverse events related to study drug and no treatment-related discontinuations. The study was not a formal non-inferiority trial and did not test a statistical hypothesis.

Planned regulatory discussions for Phase 3 in CSU and a Phase 2b food allergy trial before the end of 2025 indicate next milestones. Actual impact depends on regulatory feedback, study design, and future data disclosures.

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The information contained in this prospectus supplement is not complete and may be changed. This prospectus supplement is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-273910

SUBJECT TO COMPLETION

Dated October 21, 2025

PRELIMINARY PROSPECTUS SUPPLEMENT

(To Prospectus Dated August 17, 2023)

Shares of Common Stock

We are offering     shares of our common stock. The public offering price for each share of common stock is $   .

Our common stock is listed on the Nasdaq Global Market under the trading symbol “RAPT.” On October 20, 2025, the last reported sale price of our common stock was $33.67 per share.

We are a “smaller reporting company” as defined under the federal securities laws and, as such, have elected to comply with certain reduced public company reporting requirements for this prospectus and the documents incorporated by reference herein and may elect to comply with reduced public company reporting requirements in future filings.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described in the section titled “Risk Factors” on page S-7 of this prospectus supplement, page  8 of the accompanying prospectus and under similar headings in the documents incorporated by reference into this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

		Per share				Total
Public offering price		$				$
Underwriting discounts and commissions(1)		$				$
Proceeds to us, before expenses		$				$

(1) See the section titled “Underwriting” for additional information regarding compensation payable to the underwriters.

We have granted the underwriters an option for a period of 30 days to purchase up to an additional      shares of common stock at the public offering price, less the underwriting discounts and commissions.

The underwriters expect to deliver the shares of common stock against payment on or about October   , 2025.

Joint Bookrunning Managers

Leerink Partners TD Cowen Guggenheim Securities Wells Fargo Securities LifeSci Capital

Lead Managers

H.C. Wainwright & Co. Clear Street

October , 2025

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TABLE OF CONTENTS

Prospectus Supplement

		Page
ABOUT THIS PROSPECTUS SUPPLEMENT			S-ii
PROSPECTUS SUPPLEMENT SUMMARY			S-1
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			S-5
RISK FACTORS			S-7
USE OF PROCEEDS			S-9
DILUTION			S-10
MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES			S-12
UNDERWRITING			S-16
LEGAL MATTERS			S-29
EXPERTS			S-29
WHERE YOU CAN FIND ADDITIONAL INFORMATION			S-29
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE			S-30

Prospectus

ABOUT THIS PROSPECTUS			1
PROSPECTUS SUMMARY			3
RISK FACTORS			8
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			9
USE OF PROCEEDS			11
DESCRIPTION OF CAPITAL STOCK			12
DESCRIPTION OF DEBT SECURITIES			17
DESCRIPTION OF WARRANTS			24
LEGAL OWNERSHIP OF SECURITIES			26
PLAN OF DISTRIBUTION			29
LEGAL MATTERS			31
EXPERTS			31
WHERE YOU CAN FIND ADDITIONAL INFORMATION			31
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE			31

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a “shelf” registration statement on Form S-3 (File No. 333-273910) that we initially filed with the Securities and Exchange Commission (the “SEC”) on August 11, 2023, and that was declared effective by the SEC on August 17, 2023. This document consists of two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and also adds to and updates the information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. If there is an inconsistency between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or any document incorporated by reference prior to the date of this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. In addition, to the extent any information incorporated by reference in this prospectus supplement or the accompanying prospectus from a filing we make with the SEC after the date of this prospectus supplement adds to, updates or changes information contained in this prospectus supplement, the accompanying prospectus or an earlier filing we made with the SEC that is incorporated by reference in this prospectus supplement or the accompanying prospectus, the information in such later filing shall be deemed to modify, update and supersede such information in this prospectus supplement, the accompanying prospectus or the earlier filing with the SEC. Generally, when we refer to the prospectus, we are referring to this prospectus supplement and the accompanying prospectus combined.

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 herein 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.

We have not, and the underwriters have not, authorized anyone to provide any information other than that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus or in any free writing prospectus that we have authorized for use in connection with this offering. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to purchase, the securities offered by this prospectus supplement and the accompanying prospectus in any jurisdiction to or from any person to whom or from whom it is unlawful to make such offer or solicitation of an offer in such jurisdiction. The information contained in this prospectus supplement, the accompanying prospectus, any free writing prospectus that we have authorized for use in connection with this offering, including the documents incorporated by reference herein or therein, is accurate only as of the respective dates thereof, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or of any sale of shares of our common stock. It is important for you to read and consider all information contained in this prospectus supplement, the accompanying prospectus and any free writing prospectus that we have authorized for use in connection with this offering, including the documents incorporated by reference herein and therein, in making your investment decision. You should also read and consider the information in the documents to which we have referred you in the sections titled “Where You Can Find Additional Information” and “Incorporation of Certain Information by Reference” in this prospectus supplement and in the accompanying prospectus.

This prospectus, including the information incorporated by reference into this prospectus, include trademarks, service marks and trade names owned by us or others. All trademarks, service marks and trade names included or incorporated by reference in this prospectus or any related free writing prospectuses are the property of their respective owners.

Except as otherwise indicated herein or as the context otherwise requires, references in this prospectus supplement and accompanying prospectus to “RAPT,” “the company,” “we,” “us,” “our” and similar references refer to RAPT Therapeutics, Inc., a Delaware corporation.

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PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information appearing elsewhere in this prospectus supplement or the accompanying prospectus or incorporated by reference in this prospectus supplement or the accompanying prospectus, and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus supplement, the accompanying prospectus and any related free writing prospectus, including the risks of investing in our securities discussed in the section titled “Risk Factors” contained in this prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus supplement and the accompanying prospectus. You should also carefully read the information incorporated by reference into this prospectus supplement and the accompanying prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus supplement and the accompanying prospectus are a part.

Overview

We are a clinical-stage immunology-based biopharmaceutical company focused on discovering, developing and commercializing novel therapies for patients living with inflammatory and immunological diseases. Our lead drug candidate, RPT904, is a half-life extended monoclonal antibody (“mAb”) designed to bind free human immunoglobin E (“IgE”), a key driver of several allergic diseases.

In December 2024, we entered into an exclusive license agreement (the “Jeyou License Agreement”) with Shanghai Jeyou Pharmaceutical Co., Ltd. (“Jeyou”, formerly Shanghai Jemincare Pharmaceutical Co., Ltd.), an affiliate of Jiangxi Jemincare Group Co., Ltd., under which we have exclusive rights to develop and commercialize RPT904 worldwide, excluding mainland China, Hong Kong, Macau and Taiwan (together, the “Jeyou Territory”) and non-exclusive rights to develop and manufacture RPT904 in the Jeyou Territory for the purpose of commercializing RPT904 worldwide outside of the Jeyou Territory. Pursuant to the Jeyou License Agreement, as of the date of this prospectus supplement, our exclusive license includes one pending U.S. patent application directed to RPT904 and ten corresponding pending patent applications in Australia, Brazil, Canada, Europe (European Patent Convention), Israel, India, Japan, South Korea, New Zealand and Singapore, and our non-exclusive license for development and manufacturing purposes includes three corresponding pending patent applications in China, Hong Kong and Taiwan. We believe RPT904 could offer patients a potentially improved therapeutic option compared to omalizumab (Xolair^®), an anti-IgE antibody approved for asthma, chronic spontaneous urticaria (“CSU”), chronic rhinosinusitis with nasal polyps and food allergy. In a Phase 1 clinical trial conducted by Jeyou comparing RPT904 and omalizumab, the median half-life of RPT904 was more than two times that of omalizumab at the same dose, and RPT904 demonstrated deeper and more sustained reduction of free IgE and higher total IgE accumulation compared to omalizumab at the same dose. We plan to pursue clinical development of RPT904 initially in food allergy and CSU.

Our oncology drug candidate, tivumecirnon, is an oral small-molecule C-C motif chemokine receptor 4 antagonist designed to selectively inhibit the migration of immunosuppressive regulatory T cells into tumors. Data from a Phase 2 trial of patients with advanced checkpoint-naïve non-small cell lung cancer treated with tivumecirnon in combination with the checkpoint inhibitor pembrolizumab showed greater confirmed objective response rate and progression free survival than what has historically been demonstrated by pembrolizumab monotherapy. We hold worldwide rights to tivumecirnon, with the exception of the exclusive license (the “Hanmi License Agreement”) granted to Hanmi Pharmaceutical Ltd. in Korea, mainland China, Hong Kong, Macau and Taiwan (together, the “Hanmi Territory”). We are seeking a partner to further develop tivumecirnon outside the Hanmi Territory.

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Recent Developments

Topline Data from Jeyou’s Phase 2 Trial of RPT904 in CSU

On October 20, 2025, we and Jeyou, announced positive topline data from Jeyou’s phase 2 trial of RPT904 (JYB1904) (the “Phase 2 Trial”) as monotherapy in CSU. The Phase 2 Trial, which was conducted in China, was designed to evaluate the safety and efficacy of RPT904 at dosing intervals of 8 weeks (“Q8W”) and 12 weeks (“Q12W”) compared to omalizumab dosed every 4 weeks (“Q4W”). The Phase 2 Trial was not a formal non-inferiority study and no statistical hypothesis was tested. The data from the Phase 2 Trial indicate that RPT904 dosed Q8W or Q12W has comparable efficacy and safety to omalizumab dosed Q4W.

The randomized, double-blind Phase 2 Trial enrolled 137 adult patients with CSU inadequately controlled by H1 antihistamines for a 16-week treatment period with patients randomized 1:1:1 across three arms. Patients randomized to the RPT904 Q8W arm received 300 mg subcutaneously (“SC”) at Week 0 and Week 8, while patients randomized to the RPT904 Q12W arm received a single 300 mg SC dose at Week 0 (to represent a dosing interval of at least every 12 weeks). Patients randomized to the omalizumab Q4W arm received 300 mg SC at Weeks 0, 4, 8 and 12. The primary endpoint was change from baseline in the seven-day urticaria activity score (“UAS7”) at Weeks 8, 12 and 16, and a key secondary endpoint was the proportion of patients with UAS7=0 at Weeks 8, 12 and 16. After the initial 16-week treatment period, patients were followed for an additional 16 weeks without additional treatment. The topline data reported herein are from the initial 16-week treatment period.

The data from both the RPT904 Q8W and Q12W treatment arms showed numerically greater improvement on the UAS7 endpoint and numerically higher proportion of patients with UAS7=0 at all timepoints (Weeks 8, 12 and 16) compared to omalizumab Q4W.

The mean baseline UAS7 scores in the RPT904 Q8W, Q12W and omalizumab Q4W arms were 28.7 (±7.2), 28.9 (±6.6) and 28.8 (±7.9), respectively. The least squares mean change from baseline in UAS7 (and 95% confidence interval) at the three time points were:

		RPT904 Q8W (N=46)				RPT904 Q12W (N=46)				omalizumab Q4W (N=45)
Week 8			-20.51 (-23.88, -17.13)				-21.05 (-24.42, -17.67)				-17.00 (-20.39, -13.61)
Week 12			-22.14 (-25.46, -18.82)				-21.73 (-25.04, -18.43)				-18.51 (-21.83, -15.18)
Week 16			-23.20 (-26.49, -19.91)				-22.16 (-25.43, -18.89)				-19.14 (-22.43, -15.86)

The proportion of patients (as a percentage) with UAS7=0 (and 95% confidence interval) at the three time points were:

		RPT904 Q8W (N=46)				RPT904 Q12W (N=46)				omalizumab Q4W (N=45)
Week 8			32.61 (19.53, 48.02)				32.61 (19.53, 48.02)				31.11 (18.17, 46.65)
Week 12			36.96 (23.21, 52.45)				39.13 (25.09, 54.63)				24.44 (12.88, 39.54)
Week 16			45.65 (30.90, 60.99)				43.48 (28.93, 58.89)				33.33 (20.00, 48.95)

In the Phase 2 Trial, RPT904 was well tolerated with no serious adverse events related to study drug and no treatment-related adverse events resulting in treatment discontinuation.

We and Jeyou believe these results warrant advancing RPT904 to phase 3 development, and we plan to discuss our next steps regarding development for CSU with the U.S. Food and Drug Administration and other regulatory authorities. In addition, we anticipate initiating a phase 2b clinical trial of RPT904 in food allergies before the end of 2025.

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Corporate Information

We were incorporated under the laws of the state of Delaware in March 2015 under the name FLX Bio, Inc. In May 2019, we changed our name to RAPT Therapeutics, Inc. Our principal executive offices are located at 561 Eccles Avenue, South San Francisco, CA 94080. Our website address is www.rapt.com. Information contained on, or that can be accessed through, our website is not incorporated by reference into this prospectus supplement.

Smaller Reporting Company Status

We are a smaller reporting company as defined in the Securities Exchange Act of 1934, as amended (the “Exchange Act”). We may take advantage of certain of the scaled disclosures available to smaller reporting companies and will be able to take advantage of these scaled disclosures for so long as (i) our voting and non-voting common stock held by non-affiliates is less than $250.0 million measured on the last business day of our second fiscal quarter or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter.

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The Offering

Common stock offered by us     shares of our common stock.

Option to purchase additional shares of common stock We have granted the underwriters an option, exercisable for a period of 30 days after the date of this prospectus supplement, to purchase up to an additional    shares of common stock.

Common stock to be outstanding immediately after this offering    shares (or    shares if the underwriters exercise in full their option to purchase up to an additional    shares of our common stock).

Use of proceeds We intend to use the net proceeds from this offering, together with our existing cash, cash equivalents and marketable securities, to advance the development of RPT904 in food allergies and CSU, to support other pipeline initiatives and for working capital and general corporate purposes. See the section titled “Use of Proceeds” on page S-9 of this prospectus supplement.

Risk factors See the section titled “Risk Factors” on page S-7 for a discussion of factors you should carefully consider before deciding to invest in our common stock.

Nasdaq Global Market symbol “RAPT.”

The number of shares of common stock to be outstanding immediately after this offering is based on 16,536,069 shares of common stock outstanding as of June 30, 2025 and excludes:

• 3,391,339 shares of common stock issuable upon the exercise of options outstanding as of June 30, 2025, at a weighted average exercise price of $35.24 per share;

• 8,532,953 shares of common stock issuable upon the exercise of pre-funded warrants outstanding as of June 30, 2025 and not since exercised, at an exercise price of $0.0008 per share;

• 1,892,432 shares of common stock issued upon the exercise of pre-funded warrants subsequent to June 30, 2025;

• 62,500 shares of our common stock reserved for future issuance under the RAPT Therapeutics, Inc. Inducement Plan (the “2025 Inducement Plan”) as of June 30, 2025;

• 1,017,658 shares of our common stock reserved for future issuance under the RAPT Therapeutics, Inc. 2025 Equity Incentive Plan (the “2025 Equity Incentive Plan”) as of June 30, 2025;

• 556,346 shares of our common stock reserved for future issuance under the RAPT Therapeutics, Inc. Amended and Restated 2019 Employee Stock Purchase Plan (the “Employee Stock Purchase Plan”) as of June 30, 2025; and

• up to approximately $140.6 million of shares of common stock available for sale under the Controlled Equity Offering^SM Sales Agreement (the “ATM Sales Agreement”) with Cantor Fitzgerald & Co. and Leerink Partners LLC as of June 30, 2025.

Except as otherwise indicated, all information in this prospectus supplement assumes no exercise of outstanding options or pre-funded warrants and no exercise by the underwriters of their option to purchase from us up to an additional     shares of common stock.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the documents we have filed with the SEC that are incorporated by reference contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:

• estimates of our total addressable market, future revenue, expenses, capital requirements and our needs for additional financing;

• the initiation, cost, timing, progress and results of research and development activities, preclinical studies and clinical trials with respect to RPT904, tivumecirnon and other potential future drug candidates;

• our ability to identify, develop and commercialize drug candidates;

• our ability to advance RPT904, tivumecirnon or other future drug candidates into, and successfully complete, preclinical studies and clinical or field trials;

• our ability to obtain and maintain regulatory approval of RPT904, tivumecirnon or other future drug candidates, and any related restrictions, limitations and/or warnings in the label of an approved drug candidate;

• our ability to obtain funding for our operations and the sufficiency of such funding to support our operations;

• our ability to contract with third-party suppliers and manufacturers and their ability to perform adequately under those arrangements;

• our ability to obtain and maintain intellectual property protection for our technology and any of our drug candidates;

• our ability to successfully commercialize any of our drug candidates;

• the rate and degree of market acceptance of any of our drug candidates, including the ability of RPT904, if approved, to compete with omalizumab;

• regulatory developments in the United States and international jurisdictions;

• potential liability lawsuits and penalties related to our technology, our drug candidates and our current and future relationships with third parties;

• our ability to attract and retain key scientific and management personnel;

• our ability to effectively manage the growth of our operations;

• our ability to compete effectively with existing competitors and new market entrants;

• our expectations regarding uses of proceeds from this offering;

• potential effects of extensive government regulation;

• our financial performance;

• the volatility of the trading price of our common stock; and

• other risks and uncertainties, including those listed under the caption “Risk Factors.”

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In some cases, you can identify forward-looking statements by terms such as “anticipates,” “believes,” “could,” “estimates,” “expects,” “may,” “plans,” “potential” “predicts,” “projects,” “should,” “will,” “would,” and similar expressions intended to identify forward-looking statements. These statements reflect our current views with respect to future events and are based on assumptions and are subject to risks and uncertainties. Given these assumptions, risks and uncertainties, you should not place undue reliance on these forward-looking statements. We discuss in greater detail many of these risks in the section titled “Risk Factors” contained in the this prospectus supplement, the accompanying prospectus supplement, in any free writing prospectuses we may authorize for use in connection with a specific offering, and in our most recent Annual Report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus supplement in their entirety. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. You should read this prospectus supplement, the accompanying prospectus, together with the documents we have filed with the SEC that are incorporated by reference and any free writing prospectuses that we may authorize for use in connection with a specific offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

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RISK FACTORS

Investing in our common stock involves a high degree of risk. Before deciding whether to invest in our common stock, you should consider carefully the risks and uncertainties discussed in this section and in the sections titled Risk Factors contained in our most recent Annual Report on Form 10-K and in our subsequent Quarterly Reports on Form 10-Q for the quarterly periods ended subsequent to our filing of such Annual Report on Form 10-K, as well as any amendments or updates to our risk factors reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus supplement, together with other information in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference and any free writing prospectus that we may authorize. These risks and uncertainties are not the only risks and uncertainties we face. Additional risks and uncertainties not presently known to us, or that we currently view as immaterial, may also impair our business. If any of the risks or uncertainties described in our SEC filings or any additional risks and uncertainties actually occur, our business, financial condition, results of operations and cash flow could be materially and adversely affected. In that case, the trading price of our common stock could decline and you might lose all or part of your investment. Please also read carefully the section titled “Special Note Regarding Forward-Looking Statements.”

Risks Relating to This Offering

Raising additional capital, including as a result of this offering, may cause dilution to our stockholders, restrict our operations or require us to relinquish rights to our product candidates.

Until such time, if ever, as we can generate substantial revenue, we expect to finance our cash needs through a combination of equity offerings, debt financings and license and collaboration agreements. To the extent that we raise additional capital through the sale of equity securities, including from this offering, or convertible debt securities, your ownership interest will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect your rights as a common stockholder. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends.

If we raise additional funds through collaborations, strategic alliances or marketing, distribution or licensing arrangements with third parties, we may be required to relinquish valuable rights to our technologies, intellectual property, potential future revenue streams, or product candidates or grant licenses on terms that may not be favorable to us. If we are unable to raise additional funds through equity or debt financings or other arrangements with third parties when needed, we may be required to delay, limit, reduce or terminate our product candidate development or future commercialization efforts or grant rights to third parties to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

If you purchase shares of common stock in this offering, you will suffer immediate dilution of your investment.

The price of our common stock in this offering is substantially higher than the net tangible book value per share of our common stock. Therefore, if you purchase shares of our common stock in this offering, you will pay a price per share that substantially exceeds our net tangible book value per share after this offering. To the extent outstanding options or outstanding pre-funded warrants are exercised, you will incur further dilution. Based on the public offering price of $    per share, you will experience immediate dilution of $     per share, representing the difference between our as adjusted net tangible book value per share after giving effect to this offering and the public offering price. For additional information on the dilution that you will experience immediately after this offering, see the section titled “Dilution.”

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We have broad discretion over the use of our cash and cash equivalents, including the net proceeds we receive in this offering, and may not use them effectively.

Our management has broad discretion to use our cash and cash equivalents, including the net proceeds we receive in this offering, to fund our operations and could spend these funds in ways that do not improve our results of operations or enhance the value of our common stock. The failure by our management to apply these funds effectively could result in financial losses that could have an adverse effect on our business, cause the price of our common stock to decline and delay the development of our product candidates. Pending their use to fund operations, we may invest our cash and cash equivalents in a manner that does not produce income or that loses value.

A sale of a substantial number of shares of our common stock may cause the price of our common stock to decline.

Sales of a substantial number of shares of our common stock in the public market could occur at any time. If our stockholders sell, or the market perceives that our stockholders intend to sell, substantial amounts of our common stock in the public market, the market price of our common stock could decline significantly.

We cannot predict what effect, if any, sales of our shares in the public market or the availability of shares for sale will have on the market price of our common stock. However, future sales of substantial amounts of our common stock in the public market, including shares issued upon exercise of outstanding options or warrants, or the perception that such sales may occur, could adversely affect the market price of our common stock.

In addition, the representatives of the underwriters in this offering, may, in their sole discretion, release all or some portion of the shares subject to the lock-up agreements associated with this offering at any time and for any reason. Sales of a substantial number of such shares upon expiration of the lock-up agreements, the perception that such sales may occur, or early release of these agreements, could cause our market price to fall or make it more difficult for you to sell your common stock at a time and price that you deem appropriate.

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USE OF PROCEEDS

We estimate that we will receive net proceeds of approximately $    million from the sale of common stock offered by us in this offering, or approximately $    million if the underwriters exercise in full their option to purchase additional shares of common stock, after deducting the underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds from this offering, together with our existing cash, cash equivalents and marketable securities, to advance the development of RPT904 in food allergies and CSU, to support other pipeline initiatives and for working capital and general corporate purposes.

This expected use of the net proceeds from this offering represents our intentions based upon our current plans and business conditions. We may also use a portion of the remaining net proceeds and our existing cash, cash equivalents and marketable securities to in-license, acquire or invest in complementary businesses, technologies, products or assets. However, we have no current commitments or obligations to do so.

Based on our current operating plans, we estimate the net proceeds from this offering, together with our existing cash, cash equivalents and marketable securities, will be sufficient for us to fund our operations     . We have based this estimate on assumptions that may prove to be wrong, and we could deplete our capital resources sooner than we currently expect. Additionally, the process of conducting preclinical studies and testing product candidates in clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain. Furthermore, we may seek additional capital due to favorable market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans.

The amounts and timing of our actual expenditures will depend on numerous factors, including the factors described in the section titled “Risk Factors” in this prospectus supplement and in the documents incorporated by reference herein, 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 we will have broad discretion in the application of the net proceeds. Pending the uses described above, we plan to invest the net proceeds from this offering in short-term, interest-bearing instruments until we are ready to use them.

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DILUTION

If you invest in our common stock in this offering, your interest will be diluted immediately to the extent of the difference between the public offering price per share you will pay in this offering and the as adjusted net tangible book value per share of our common stock after this offering. Our historical net tangible book value as of June 30, 2025 was $165.3 million, or $9.99 per share of common stock. Historical net tangible book value per share represents the amount of our total tangible assets less total liabilities, divided by the number of shares of our common stock outstanding on June 30, 2025.

After giving effect to our issuance and sale of      shares of common stock in this offering at the public offering price of $     per share, and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of June 30, 2025 would have been $     million, or $     per share. This represents an immediate increase in as adjusted net tangible book value per share of $     to existing stockholders and immediate dilution of $     in as adjusted net tangible book value per share to new investors purchasing common stock in this offering. Dilution per share to new investors is determined by subtracting as adjusted net tangible book value per share after this offering from the public offering price per share paid by new investors. The following table illustrates this per share dilution to the new investors purchasing common stock in this offering without giving effect to the option to purchase additional shares granted to the underwriters:

Public offering price per share						$
Net tangible book value per share as of June 30, 2025		$	9.99
Increase per share attributable to sale of shares of common stock in this offering
As adjusted net tangible book value per share after this offering
Dilution per share to new investors						$

If the underwriters exercise their option to purchase      additional shares in full at the public offering price of $     per share, the as adjusted net tangible book value will increase to $     per share, representing an immediate increase to existing stockholders of $     per share and an immediate dilution of $     per share to new investors.

Except as noted above, the above discussion and table are based on 16,536,069 shares of our common stock outstanding as of June 30, 2025, and excludes:

• 3,391,339 shares of common stock issuable upon the exercise of options outstanding as of June 30, 2025, at a weighted average exercise price of $35.24 per share;

• 8,532,953 shares of common stock issuable upon the exercise of pre-funded warrants outstanding as of June 30, 2025 and not since exercised, at an exercise price of $0.0008 per share;

• 1,892,432 shares of common stock issued upon the exercise of pre-funded warrants subsequent to June 30, 2025;

• 62,500 shares of our common stock reserved for future issuance under the Inducement Plan as of June 30, 2025;

• 1,017,658 shares of our common stock reserved for future issuance under the 2025 Equity Incentive Plan as of June 30, 2025;

• 556,346 shares of our common stock reserved for future issuance under the Employee Stock Purchase Plan as of June 30, 2025; and

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• up to approximately $140.6 million of shares of common stock available for sale under the ATM Sales Agreement as of June 30, 2025.

To the extent that any options or pre-funded warrants are exercised, new stock awards are issued under our equity incentive plans or we otherwise issue additional shares of common stock in the future at a price less than the public offering price, there may be further dilution to new investors purchasing common stock in this offering.

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES TO NON-U.S. HOLDERS

The following is a general discussion of the material U.S. federal income tax considerations to non-U.S. holders (as defined below) of the purchase, ownership and disposition of shares of our common stock issued pursuant to this offering, or the shares. All prospective holders of the shares should consult their tax advisors with respect to the U.S. federal, state, and local and non-U.S. tax consequences of the purchase, ownership and disposition of the shares.

This discussion is not a complete analysis of all potential U.S. federal income tax consequences relating to the purchase, ownership and disposition of the shares. This discussion is based on current provisions of the U.S. Internal Revenue Code of 1986, as amended, or the Code, existing U.S. Treasury Regulations promulgated thereunder, published administrative pronouncements and rulings of the U.S. Internal Revenue Service, or the IRS, and judicial decisions, all as in effect as of the date of this prospectus supplement. These authorities are subject to change and to differing interpretation, possibly with retroactive effect. Any change or differing interpretation could alter the tax consequences to non-U.S. holders described in this discussion. There can be no assurance that a court or the IRS will not challenge one or more of the tax consequences described herein, and we have not obtained, nor do we intend to obtain, a ruling with respect to the U.S. federal income tax consequences to a non-U.S. holder of the purchase, ownership or disposition of the shares.

We assume in this discussion that a non-U.S. holder holds the shares as a “capital asset” within the meaning of Section 1221 of the Code (generally, property held for investment). This discussion does not address all aspects of U.S. federal income taxation that may be relevant to a particular non-U.S. holder in light of that holder’s individual circumstances, nor does it address any alternative minimum, Medicare contribution, estate or gift tax consequences, any aspects of U.S. state or local or non-U.S. taxes or any other U.S. federal tax laws, or the special accounting rules in Section 451(b) of the Code. This discussion also does not address consequences relevant to non-U.S. holders subject to special tax rules, such as non-U.S. holders that own, or are deemed to own, more than 5% of our capital stock (except to the extent specifically set forth below), corporations that accumulate earnings to avoid U.S. federal income tax, tax-exempt organizations, governmental organizations, banks, financial institutions, investment funds, insurance companies, brokers, dealers or traders in securities, commodities or currencies, tax-qualified retirement plans, non-U.S. holders who hold or receive the shares pursuant to the exercise of employee stock options or otherwise as compensation, non-U.S. holders holding the shares as part of a hedge, straddle or other risk reduction strategy, conversion transaction or other integrated investment, non-U.S. holders deemed to sell the shares under the constructive sale provisions of the Code, controlled foreign corporations, passive foreign investment companies and certain former U.S. citizens or long-term residents.

In addition, this discussion does not address the tax treatment of partnerships (or entities or arrangements that are treated as partnerships or disregarded entities for U.S. federal income tax purposes) or persons that hold the shares through such partnerships. If a partnership, including any entity or arrangement treated as a partnership for U.S. federal income tax purposes, holds the shares, the U.S. federal income tax treatment of a partner in such partnership generally will depend upon the status of the partner, the activities of the partnership and certain determinations made at the partner level. Such partners and partnerships should consult their tax advisors regarding the tax consequences of the purchase, ownership and disposition of the shares.

Definition of Non-U.S. Holder

In general, a “non-U.S. holder” means a beneficial owner of the shares that is neither a partnership or an entity or arrangement treated as a partnership for U.S. federal income tax purposes nor, for U.S. federal income tax purposes:

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

• a corporation, or an entity treated as a corporation for U.S. federal income tax purposes, created or organized in the United States or under the laws of the United States or of any state thereof or the District of Columbia;

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• an estate, the income of which is subject to U.S. federal income tax regardless of its source; or

• a trust if (a) a U.S. court can exercise primary supervision over the trust’s administration and one or more U.S. persons (as defined in the Code) have the authority to control all of the trust’s substantial decisions or (b) the trust has a valid election in effect under applicable U.S. Treasury Regulations to be treated as a U.S. person.

Distributions on the Shares

We do not anticipate paying any cash dividends in the foreseeable future. However, if we make distributions on the shares, such distributions will constitute dividends to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a tax-free return of the non-U.S. holder’s investment, up to such non-U.S. holder’s adjusted tax basis in the shares. Any remaining excess will be treated as capital gain from the sale or exchange of such shares, subject to the tax treatment described below in “—Gain on Sale, Exchange or Other Taxable Disposition of the Shares.”

Dividends paid to a non-U.S. holder will generally be subject to withholding of U.S. federal income tax at a 30% rate of the gross amount of the dividend or such lower rate as may be specified by an applicable income tax treaty between the United States and such non-U.S. holder’s country of residence for purposes of such treaty.

Dividends that are treated as effectively connected with a trade or business conducted by a non-U.S. holder within the United States and, if an applicable income tax treaty so provides, that are attributable to a permanent establishment or a fixed base maintained by the non-U.S. holder within the United States, are generally exempt from the 30% withholding tax if the non-U.S. holder satisfies applicable certification and disclosure requirements. However, such U.S. effectively connected income, net of specified deductions and credits, is taxed at the same U.S. federal income tax rates applicable to U.S. persons. Any U.S. effectively connected income received by a non-U.S. holder that is a corporation may also, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate or such lower rate as may be specified by an applicable income tax treaty between the United States and such non-U.S. holder’s country of residence for purposes of such treaty.

To claim a reduction or exemption from withholding, a non-U.S. holder generally will be required to provide (a) a properly executed IRS Form W-8BEN or IRS Form W-8BEN-E (or successor form) and satisfy applicable certification and other requirements to claim the benefit of an applicable income tax treaty between the United States and such non-U.S. holder’s country of residence, or (b) a properly executed IRS Form W-8ECI stating that the dividends are not subject to withholding because they are effectively connected with such non-U.S. holder’s conduct of a trade or business within the United States. Non-U.S. holders are urged to consult their tax advisors regarding their entitlement to benefits under a relevant income tax treaty.

A non-U.S. holder that is eligible for a reduced rate of U.S. withholding tax under an income tax treaty may obtain a refund or credit of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS.

Distributions will also be subject to the discussion below under the headings “—Backup Withholding and Information Reporting” and “—Foreign Accounts.”

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Gain on Sale, Exchange or Other Taxable Disposition of the Shares

Subject to the discussion below under the headings “—Backup Withholding and Information Reporting” and “—Foreign Accounts,” in general, a non-U.S. holder will not be subject to any U.S. federal income tax on any gain realized upon such non-U.S. holder’s sale, exchange or other taxable disposition of the shares unless:

• the gain is effectively connected with a U.S. trade or business of the non-U.S. holder and, if an applicable income tax treaty so provides, is attributable to a permanent establishment or a fixed base maintained in the United States by such non-U.S. holder, in which case the non-U.S. holder generally will be taxed at the U.S. federal income tax rates applicable to U.S. persons and, if the non-U.S. holder is a foreign corporation, the branch profits tax described above in “—Distributions on the Shares” also may apply;

• the non-U.S. holder is a nonresident alien individual who is present in the United States for 183 days or more in the taxable year of the disposition and certain other conditions are met, in which case the non-U.S. holder will be subject to a 30% U.S. federal income tax (or such lower rate as may be specified by an applicable income tax treaty) on the net gain derived from the disposition, which may be offset by U.S. source capital losses of the non-U.S. holder, if any (even though the individual is not considered a resident of the United States); or

• we are, or have been, at any time during the five-year period preceding such disposition (or the non-U.S. holder’s holding period, if shorter) a “U.S. real property holding corporation,” in which case such non-U.S. holder generally will be taxed on its net gain derived from the disposition as effectively connected income taxable at the U.S. federal income tax rates applicable to U.S. persons; however, the branch profits tax described above will not apply to a U.S. holder that is a foreign corporation. Generally, a corporation is a U.S. real property holding corporation if the fair market value of its U.S. real property interests equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests plus its other assets used or held for use in a trade or business. Although there can be no assurance, we do not believe that we are currently, and do not anticipate becoming, a U.S. real property holding corporation. Even if we are or become a U.S. real property holding corporation, provided that our common stock is regularly traded, as defined by applicable U.S. Treasury Regulations, on an established securities market, the shares will be treated as a U.S. real property interest only with respect to a non-U.S. holder that holds more than 5% of the shares (as determined under U.S. federal income tax principles), directly or indirectly, actually or constructively, during the shorter of the 5-year period ending on the date of the disposition or the period that the non-U.S. holder held the shares. There can be no assurance that our common stock will qualify as regularly traded on an established securities market.

Backup Withholding and Information Reporting

We must report annually to the IRS and to each non-U.S. holder the gross amount of the distributions on the shares paid to such non-U.S. holder and the tax withheld, if any, with respect to such distributions. Non-U.S. holders will have to comply with specific certification procedures to establish that the holder is not a U.S. person in order to avoid backup withholding at the applicable rate with respect to any dividends on the shares. A non-U.S. holder generally will not be subject to U.S. backup withholding with respect to payments of distributions on the shares if it certifies its non-U.S. status by providing a valid IRS Form W-8BEN or IRS Form W-8BEN-E (or successor form) or IRS Form W-8ECI, or otherwise establishes an exemption; provided that we do not have actual knowledge or reason to know such non-U.S. holder is a U.S. person. Distributions paid to non-U.S. holders subject to the U.S. withholding tax, as described above in “—Distributions on the Shares” generally will be exempt from U.S. backup withholding.

Information reporting and backup withholding generally will apply to the proceeds of a disposition of the shares by a non-U.S. holder effected by or through the U.S. office of any broker, U.S. or foreign, unless the holder certifies its status as a non-U.S. holder and satisfies certain other requirements, or otherwise establishes an exemption.

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Copies of information returns may be made available to the tax authorities of the country in which the non-U.S. holder resides or is established under the provisions of a specific treaty or agreement.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules from a payment to a non-U.S. holder may be allowed as a credit against the non-U.S. holder’s U.S. federal income tax liability, if any, and may entitle such holder to a refund, provided that the required information is timely furnished to the IRS.

Foreign Accounts

The Code generally imposes a U.S. federal withholding tax of 30% on dividends and, subject to the discussion below regarding proposed regulations issued by the U.S. Treasury Department, the gross proceeds of a disposition of the shares paid to a “foreign financial institution” (as defined in the Code), unless such institution enters into an agreement with the U.S. government to, among other things, withhold on certain payments and to collect and provide to the U.S. tax authorities substantial information regarding accounts held by certain “specific United States persons” or “United States owned foreign entities” (each as defined in the Code), or otherwise qualifies for an exemption from these rules. A U.S. federal withholding tax of 30% also applies to dividends and, subject to the discussion below regarding proposed regulations issued by the U.S. Treasury Department, will apply to the gross proceeds of a disposition of the shares paid to a “non-financial foreign entity” (as defined in the Code), unless such entity provides the withholding agent with either a certification that it does not have any “substantial United States owners” (as defined in the Code), provides information regarding each substantial United States owners of the entity, or otherwise qualifies for an exemption from these rules. Under certain circumstances, a non-U.S. holder might be eligible for refunds or credits of such taxes. An intergovernmental agreement between the United States and an applicable foreign country may modify the requirements described in this paragraph.

The withholding provisions described above currently apply to dividends paid on the shares. The U.S. Treasury Department released proposed regulations which, if finalized in their present form, would eliminate the U.S. federal withholding tax of 30% applicable to the gross proceeds of a sale or other disposition of the shares. In its preamble to such proposed regulations, the U.S. Treasury Department stated that taxpayers may generally rely on the proposed regulations until final regulations are issued.

EACH PROSPECTIVE INVESTOR SHOULD CONSULT ITS TAX ADVISOR REGARDING THE PARTICULAR U.S. FEDERAL, STATE AND LOCAL AND NON-U.S. TAX CONSEQUENCES OF PURCHASING, HOLDING AND DISPOSING OF THE SHARES, INCLUDING THE CONSEQUENCES OF ANY PROPOSED CHANGE IN APPLICABLE LAWS.

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UNDERWRITING

Leerink Partners LLC, TD Securities (USA) LLC, Guggenheim Securities, LLC, Wells Fargo Securities, LLC and LifeSci Capital LLC are acting as representatives of each of the underwriters named below and as joint bookrunning managers for this offering. Subject to the terms and conditions set forth in the underwriting agreement among us and the underwriters, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the number of shares of common stock set forth opposite its name below.

Underwriter		Number of Shares
Leerink Partners LLC
TD Securities (USA) LLC
Guggenheim Securities, LLC
Wells Fargo Securities, LLC
LifeSci Capital LLC
H.C. Wainwright & Co., LLC
Clear Street LLC
Total

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the shares of our common stock sold under the underwriting agreement if any of the shares of our common stock 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 against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the shares of our common stock, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel, including the validity of the shares, and subject to other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officers’ certificates and legal opinions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Discounts and Commissions

The representatives have advised us that the underwriters propose initially to offer the shares to the public at the initial public offering price set forth on the cover page of this prospectus supplement and to dealers at that price less a concession not in excess of $    per share. After the initial offering of the shares of our common stock, the public offering price, concession or any other term of this offering may be changed by the representatives.

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The following table shows the initial public offering price, underwriting discounts and commissions and proceeds, before expenses, to us. The information assumes either no exercise or full exercise by the underwriters of their option to purchase additional shares of our common stock.

Total

Per Share

Without Option

With Option

Initial public offering price

$

$

$

Underwriting discounts and commissions

$

$

$

Proceeds, before expenses, to us

$

$

$

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

Option to Purchase Additional Shares

We have granted an option to the underwriters, exercisable for 30 days after the date of this prospectus supplement, to purchase from us up to an additional      shares of our common stock, at the initial public offering price, less underwriting discounts and commissions. If the underwriters exercise this option, each underwriter will be obligated, subject to the conditions contained in the underwriting agreement, to purchase a number of additional shares proportionate to that underwriter’s initial amount reflected in the above table.

No Sales of Similar Securities

We have agreed with the underwriters that we will not (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, or submit to, or file with the SEC, a registration statement under the Securities Act relating to, any shares of our common stock or any securities convertible into or exercisable or exchangeable for any shares of our common stock, or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of any shares of common stock or any such other securities, or publicly disclose the intention to undertake any of the transactions described in (i) or (ii) (regardless of whether any of these transactions are to be settled by the delivery of shares of common stock or such other securities, in cash or otherwise), in each case without the prior written consent of the representatives of the underwriters, for a period of 60 days after the date of this prospectus supplement, other than the securities to be sold hereunder, any shares of our common stock issued upon the exercise (including any net exercise or exercise by delivery of already-owned shares of our common stock) of an option or warrant or the settlement of restricted stock units or the conversion of a security outstanding on the date of this prospectus supplement and as described herein, any shares issued upon exercise of the pre-funded warrants outstanding on the date of this prospectus supplement and as described herein, any shares of our common stock issued or options to purchase common stock or restricted stock units covering shares of common stock granted pursuant to our existing employee benefit plans referred to herein, any shares of our common stock issued or options to purchase our common stock granted pursuant to any non-employee director stock plan referred to herein, the filing by us of any registration statement on Form S-8 or a successor form thereto with respect to the registration of securities to be offered under any employee benefit or equity incentive plan referred to herein, shares sold pursuant to the ATM Sales Agreement following the earlier to occur of (i) the date that is 30 days following the date of this prospectus and (ii) the date that the underwriters exercise in full their option to purchase additional shares, provided that we will not sell shares under the ATM Sales Agreement at a price below the public offering price per share of common stock in this offering, or shares of our common stock or other securities issued by us in connection with a transaction that includes a commercial relationship (including license arrangements, strategic alliances, commercial lending relationships, joint ventures and strategic acquisitions), provided that (i) the aggregate number of shares issued pursuant to such a transaction does not exceed 5.0% of the total number of outstanding shares of our common stock immediately following the issuance and sale of the securities and (ii) in each case, the recipient of any such shares issued in the circumstances listed above shall enter into a lock-up agreement.

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Our directors and executive officers have entered into lock-up agreements with the underwriters prior to the commencement of this offering pursuant to which each of these persons or entities, with limited exceptions and for a period of 60 days after the date of this prospectus supplement, may not, without the prior written consent of the representatives of the underwriters, (1) 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 shares of our common stock or any securities convertible into or exercisable or exchangeable for our common stock (including, without limitation, common stock or such other securities which may be deemed to be beneficially owned by such directors and executive officers in accordance with the rules and regulations of the SEC and securities which may be issued upon exercise of a stock option or warrant) or (2) enter into any hedging, swap or other agreement or transaction that transfers, in whole or in part, any of the economic consequences of ownership of the common stock or such other securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of common stock or such other securities, in cash or otherwise, (3) make any demand for or exercise any right with respect to the registration of any shares of our common stock or any security convertible into or exercisable or exchangeable for our common stock or (4) publicly disclose the intention to do any of the foregoing.

The restrictions described in the immediately preceding paragraph are subject to specified exceptions, including among other items:

• transfers of shares of our common stock (i) as a bona fide gift or gifts, including to charitable organizations or for bona fide estate planning purposes, (ii) by will or intestate succession upon the death of the person, including to the transferee’s nominee or custodian; (iii) to the immediate family of the person or any trust, partnership or similar entity for the direct or indirect benefit of the person or the immediate family of the person, (iv) as a distribution to the person’s limited partners or stockholders, or (v) to the person’s affiliates or any investment fund or other entity controlled or managed by the person, and, if the person is a trust, to a trustor, trustee (or co-trustee) or beneficiary of the trust or to the estate of the beneficiary of such trust, provided that for clauses (i), (ii) and (iii), any required public report or filing (including filings under Section 16(a) of the Exchange Act) shall disclose the nature of such transfer and that the transfered securities remain subject to the lock-up agreement and that for clauses (iv) and (v), such transfers are not required to be reported with the SEC on Form 4 in accordance with Section 16(a) of the Exchange Act;

• transfers of shares of our common stock to us upon exercise of any option granted under our incentive plans, including the surrender of shares of common stock to us in “net” or “cashless” exercise of any option, provided that (1) the shares of common stock received by the person upon exercise continue to be subject to the restrictions on transfer set forth in the lock-up agreement, and (2) if required, any public report or filing under Section 16 of the Exchange Act shall clearly indicate in the footnotes thereto that the filing relates to the exercise of a stock option that no shares were sold by the reporting person and that the shares received upon exercise of the stock option are subject to a lock-up agreement with the underwriters;

• transfers of shares of our common stock to us in connection with our repurchase of shares of common stock pursuant to a repurchase right arising upon the termination of the person’s employment with us, provided that such repurchase right is pursuant to contractual agreements with us; provided further that any filing required by Section 16 of the Exchange Act shall clearly indicate in the footnotes thereto that the such transfer is being made pursuant to the circumstances described in this clause; and provided further that no other public announcement or filing shall be required or shall be voluntarily made during the restricted period;

• transfers of shares of our common stock pursuant to an order of a court of competent jurisdiction or in connection with a qualified domestic order or divorce settlement, provided that each transferee agrees in writing to be bound by the terms of the lock-up agreement prior to such transfer; and provided further, that any filing required by Section 16 of the Exchange Act shall clearly indicate in the footnotes thereto that the such transfer is being made pursuant to the circumstances described in this clause;

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• sales or transfers of shares of our common stock pursuant to a 10b5-1 trading plan that complies with Rule 10b5-1 under the Exchange Act in effect on the date of this prospectus and disclosed to the representatives prior to such date, provided that any filing under Section 16 of the Exchange Act made in connection with such sales shall clearly indicate in the footnotes thereto that such disposition of shares of common stock was pursuant to a 10b5-1 plan;

• the establishment of a trading plan pursuant to Rule 10b5-1 under the Exchange Act, provided that no sales of common stock are made under such plans during the restricted period, and further provided that the establishment of a 10b5-1 trading plan or the amendment of a 10b5-1 trading plan shall only be permitted if no filing by any party under the Exchange Act or other public announcement shall be made in connection with such trading plan during the restricted period, except as required by law or regulation, provided that to the extent a filing under the Exchange Act or other public announcement is required by law or regulation, such filing or announcement shall include a statement to the effect that no transfers may be made pursuant to such 10b5-1 trading plan during the restricted period; and

• sales in connection with this offering pursuant to the terms of the underwriting agreement.

The representatives, in their sole discretion, may release the securities subject to the lock-up agreements described above in whole or in part at any time with or without notice.

Nasdaq Global Market Listing

Our common stock is listed on the Nasdaq Global Market under the symbol “RAPT”.

Price Stabilization, Short Positions and Penalty Bids

Until the distribution of the shares is completed, SEC rules may limit underwriters and selling group members from bidding for and purchasing our common stock. However, the representatives may engage in transactions that stabilize the price of the common stock, such as bids or purchases to peg, fix or maintain that price.

In connection with this offering, the underwriters may purchase and sell our common stock in the open market. These transactions may include short sales, purchases on the open market to cover positions created by short sales and stabilizing transactions. Short sales involve the sale by the underwriters of a greater number of shares than they are required to purchase in this offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares described above. The underwriters may close out any covered short position by either exercising their option to purchase additional shares or purchasing 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 shares granted to them under the underwriting agreement described above. “Naked” short sales are sales in excess of such option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our common stock in the open market after pricing that could adversely affect investors who purchase in this offering. Stabilizing transactions consist of various bids for or purchases of shares of common stock made by the underwriters in the open market prior to the closing of this offering.

The underwriters may also impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the representatives have repurchased shares sold by or for the account of such underwriter in stabilizing or short covering transactions.

Similar to other purchase transactions, the underwriters’ purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on the Nasdaq Global Market, in the over-the-counter market or otherwise.

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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 stock. In addition, neither we nor any of the underwriters make any representation that the representatives will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Electronic Distribution

In connection with this offering, certain of the underwriters or securities dealers may distribute prospectuses by electronic means, such as e-mail.

Other Relationships

The underwriters and certain of their 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. Some of the underwriters and certain of their affiliates may in the future engage in investment banking and other commercial dealings in the ordinary course of business with us and our affiliates, for which they may in the future receive customary fees, commissions and expenses. Leerink Partners LLC is an agent under our ATM Sales Agreement. Under the ATM Sales Agreement, we may offer and sell, from time to time, shares of our common stock through Leerink Partners LLC through an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act.

In addition, in the ordinary course of their business activities, the underwriters and their 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. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Selling Restrictions

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area (each a “Relevant State”), no securities have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the securities which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that offers of securities may be made to the public in that Relevant 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 Article 2 of the Prospectus Regulation;

(b) to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of 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 securities shall require us or any underwriter 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 securities or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with each of the underwriters and the Company that it is a “qualified investor” within the meaning of Article 2(e) of the Prospectus Regulation. In the case of any securities being offered to a

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financial intermediary as that term is used in the Prospectus Regulation, each such financial intermediary will be deemed to have represented, acknowledged and agreed that the securities 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 securities to the public other than their offer or resale in a Relevant State to qualified investors as so defined or in circumstances in which the prior consent of the underwriters have 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 securities in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any securities to be offered so as to enable an investor to decide to purchase or subscribe for any securities, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

Notice to Prospective Investors in the United Kingdom

No securities have been offered or will be offered pursuant to the offering to the public in the United Kingdom prior to the publication of a prospectus in relation to the securities which is to be treated as if it had been approved by the Financial Conduct Authority in accordance with the transitional provisions in Article 74 (transitional provisions) of the Prospectus Amendment etc (EU Exit) Regulations 2019/1234, except that the Shares may be offered to the public in the United Kingdom at any time:

(a) to any legal entity which is a qualified investor as defined under Article 2 of the UK Prospectus Regulation;

(b) to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the UK Prospectus Regulation), subject to obtaining the prior consent of underwriters for any such offer; or

(c) in any other circumstances falling within Section 86 of the FSMA.

provided that no such offer of the securities shall require the Issuer or any Manager to publish a prospectus pursuant to Section 85 of the FSMA or supplement a prospectus pursuant to Article 23 of the UK Prospectus Regulation. For the purposes of this provision, the expression an “offer to the public” in relation to the securities in the United Kingdom means the communication in any form and by any means of sufficient information on the terms of the offer and any securities to be offered so as to enable an investor to decide to purchase or subscribe for any securities and the expression “UK Prospectus Regulation” means Regulation (EU) 2017/1129 as it forms part of domestic law by virtue of the European Union (Withdrawal) Act 2018.

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 (all such persons together being referred to as “relevant persons”) or otherwise in circumstances which have not resulted and will not result in an offer to the public of the securities 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.

Notice to prospective investors in Hong Kong

The securities 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

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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 securities 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 securities 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.

Notice to prospective investors in Japan

The securities have not been and will not be registered pursuant to Article 4, Paragraph 1 of the Financial Instruments and Exchange Act. Accordingly, none of the securities nor any interest therein may be offered or sold, directly or indirectly, 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 resale, directly or indirectly, in Japan or to or for the benefit of a resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the Financial Instruments and Exchange Act and any other applicable laws, regulations and ministerial guidelines of Japan in effect at the relevant time.

Notice to prospective investors in Switzerland

This prospectus does not constitute an offer to the public or a solicitation to purchase or invest in any securities. No securities have been offered or will be offered to the public in Switzerland, except that offers of securities may be made to the public in Switzerland at any time under the following exemptions under the Swiss Financial Services Act (“FinSA”):

(a) to any person which is a professional client as defined under the FinSA;

(b) to fewer than 500 persons (other than professional clients as defined under the FinSA), subject to obtaining the prior consent of the underwriters for any such offer; or

(c) in any other circumstances falling within Article 36 FinSA in connection with Article 44 of the Swiss Financial Services Ordinance,

provided that no such offer of securities shall require the Company or any underwriter to publish a prospectus pursuant to Article 35 FinSA.

The securities have not been and will not be listed or admitted to trading on a trading venue in Switzerland.

Neither this document nor any other offering or marketing material relating to the securities constitutes a prospectus as such term is understood pursuant to the FinSA and neither this document nor any other offering or marketing material relating to the securities may be publicly distributed or otherwise made publicly available in Switzerland.

Notice to prospective investors in Israel

In the State of Israel this prospectus supplement shall not be regarded as an offer to the public to purchase securities under the Israeli Securities Law, 5728—1968, which requires a prospectus to be published and authorized by the Israel Securities Authority, if it complies with certain provisions of Section 15 of the Israeli Securities Law, 5728–1968, including, inter alia, if: (i) the offer is made, distributed or directed to not more than 35 investors, subject to certain conditions, or the Addressed Investors; or (ii) the offer is made, distributed or

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directed to certain qualified investors defined in the First Addendum of the Israeli Securities Law, 5728—1968, subject to certain conditions, or the “Qualified Investors.” The Qualified Investors shall not be taken into account in the count of the Addressed Investors and may be offered to purchase securities in addition to the 35 Addressed Investors. We have not and will not take any action that would require us to publish a prospectus in accordance with and subject to the Israeli Securities Law, 5728—1968. We have not and will not distribute this prospectus supplement or make, distribute or direct an offer to subscribe for our shares of common stock to any person within the State of Israel, other than to Qualified Investors and up to 35 Addressed Investors. Qualified Investors may have to submit written evidence that they meet the definitions set out in of the First Addendum to the Israeli Securities Law, 5728—1968. In particular, we may request, as a condition to be offered securities, that Qualified Investors will each represent, warrant and certify to us and/or to anyone acting on our behalf: (i) that it is an investor falling within one of the categories listed in the First Addendum to the Israeli Securities Law, 5728—1968; (ii) which of the categories listed in the First Addendum to the Israeli Securities Law, 5728—1968 regarding Qualified Investors is applicable to it; (iii) that it will abide by all provisions set forth in the Israeli Securities Law, 5728—1968 and the regulations promulgated thereunder in connection with the offer to be issued securities; (iv) that the securities that it will be issued are, subject to exemptions available under the Israeli Securities Law, 5728—1968: (a) for its own account; (b) for investment purposes only; and (c) not issued with a view to resale within the State of Israel, other than in accordance with the provisions of the Israeli Securities Law, 5728—1968; and (v) that it is willing to provide further evidence of its Qualified Investor status. Addressed Investors may have to submit written evidence in respect of their identity and may have to sign and submit a declaration containing, inter alia, the Addressed Investor’s name, address and passport number or Israeli identification number.

Notice to prospective investors in Singapore

Each underwriter has acknowledged that this prospectus supplement and the accompanying prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, each underwriter has represented and agreed that it has not offered or sold any securities or caused the securities to be made the subject of an invitation for subscription or purchase and will not offer or sell any securities or cause the securities 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 and the accompanying prospectus or any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the securities, 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 securities 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 (howsoever described) in that trust shall not be transferred

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within six months after that corporation or that trust has acquired the securities 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)(c)(ii) of the SFA;

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

(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.

Notice to Prospective Investors in China

This prospectus supplement will not be circulated or distributed in the PRC and the securities will not be offered or sold, and will not be offered or sold to any person for re-offering or resale directly or indirectly to any residents of the PRC (for such purposes, not including the Hong Kong and Macau Special Administrative Regions or Taiwan) except pursuant to any applicable laws and regulations of the PRC. Neither this prospectus supplement nor any advertisement or other offering material may be distributed or published in the PRC, except under circumstances that will result in compliance with applicable laws and regulations.

Notice to Prospective Investors in Korea

The securities have not been and will not be registered under the Financial Investments Services and Capital Markets Act of Korea and the decrees and regulations thereunder (the “FSCMA”), and the securities have been and will be offered in Korea as a private placement under the FSCMA. None of the securities may be offered, sold or delivered directly or indirectly, or offered or sold to any person for re-offering or resale, directly or indirectly, in Korea or to any resident of Korea except pursuant to the applicable laws and regulations of Korea, including the FSCMA and the Foreign Exchange Transaction Law of Korea and the decrees and regulations thereunder (the “FETL”). The securities have not been listed on any of securities exchanges in the world including, without limitation, the Korea Exchange in Korea. Furthermore, the purchaser of the securities shall comply with all applicable regulatory requirements (including but not limited to requirements under the FETL) in connection with the purchase of the securities. By the purchase of the securities, the relevant holder thereof will be deemed to represent and warrant that if it is in Korea or is a resident of Korea, it purchased the securities pursuant to the applicable laws and regulations of Korea.

Notice to Prospective Investors in Malaysia

No prospectus or other offering material or document in connection with the offer and sale of the securities has been or will be registered with the Securities Commission of Malaysia (“Commission”) for the Commission’s approval pursuant to the Capital Markets and Services Act 2007. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the securities may not be circulated or distributed, nor may the securities be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Malaysia other than (i) a closed end fund approved by the Commission; (ii) a holder of a Capital Markets Services Licence; (iii) a person who acquires the securities, as principal, if the offer is on terms that the securities may only be acquired at a consideration of not less than RM250,000 (or its equivalent in foreign currencies) for each transaction; (iv) an individual whose total net personal assets or total net joint assets with his or her spouse exceeds RM3 million (or its equivalent in foreign currencies), excluding the value of the primary residence of the individual; (v) an individual who has a gross annual income exceeding RM300,000 (or its equivalent in foreign currencies) per annum in the preceding twelve months; (vi) an individual who, jointly with his or her spouse, has

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a gross annual income of RM400,000 (or its equivalent in foreign currencies), per annum in the preceding twelve months; (vii) a corporation with total net assets exceeding RM10 million (or its equivalent in a foreign currencies) based on the last audited accounts; (viii) a partnership with total net assets exceeding RM10 million (or its equivalent in foreign currencies); (ix) a bank licensee or insurance licensee as defined in the Labuan Financial Services and Securities Act 2010; (x) an Islamic bank licensee or takaful licensee as defined in the Labuan Financial Services and Securities Act 2010; and (xi) any other person as may be specified by the Commission; provided that, in the each of the preceding categories (i) to (xi), the distribution of the securities is made by a holder of a Capital Markets Services Licence who carries on the business of dealing in securities. The distribution in Malaysia of this prospectus supplement is subject to Malaysian laws. This prospectus supplement does not constitute and may not be used for the purpose of public offering or an issue, offer for subscription or purchase, invitation to subscribe for or purchase any securities requiring the registration of a prospectus with the Commission under the Capital Markets and Services Act 2007.

Notice to Prospective Investors in Taiwan

The securities have not been and will not be registered with the Financial Supervisory Commission of Taiwan pursuant to relevant securities laws and regulations and may not be sold, issued or offered within Taiwan through a public offering or in circumstances which constitutes an offer within the meaning of the Securities and Exchange Act of Taiwan that requires a registration or approval of the Financial Supervisory Commission of Taiwan. No person or entity in Taiwan has been authorized to offer, sell, give advice regarding or otherwise intermediate the offering and sale of the securities in Taiwan.

Notice to Prospective Investors in Saudi Arabia

This prospectus supplement may not be distributed in the Kingdom of Saudi Arabia except to such persons as are permitted under the Rules on the Offer of Securities and Continuing Obligations Regulations as issued by the board of the Saudi Arabian Capital Market Authority (“CMA”) pursuant to resolution number 3-123-2017 dated 27 December 2017, as amended (the “CMA Regulations”). The CMA does not make any representation as to the accuracy or completeness of this document and expressly disclaims any liability whatsoever for any loss arising from, or incurred in reliance upon, any part of this document. Prospective purchasers of the securities offered hereby should conduct their own due diligence on the accuracy of the information relating to the securities. If you do not understand the contents of this document, you should consult an authorized financial adviser.

Notice to prospective investors in Australia

This prospectus supplement:

• does not constitute a disclosure document or a prospectus under Chapter 6D.2 of the Corporations Act 2001 (Cth) (the “Corporations Act”);

• has not been, and will not be, lodged with the Australian Securities and Investments Commission (“ASIC”), as a disclosure document for the purposes of the Corporations Act and does not purport to include the information required of a disclosure document for the purposes of the Corporations Act; and

• may only be provided in Australia to select investors who are able to demonstrate that they fall within one or more of the categories of investors, available under section 708 of the Corporations Act (“Exempt Investors”).

The securities may not be directly or indirectly offered for subscription or purchased or sold, and no invitations to subscribe for or buy the securities may be issued, and no draft or definitive offering memorandum, advertisement or other offering material relating to any securities may be distributed in Australia, except where disclosure to investors is not required under Chapter 6D of the Corporations Act or is otherwise in compliance with all applicable Australian laws and regulations. By submitting an application for the securities, you represent and warrant to us that you are an Exempt Investor.

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As any offering of securities under this prospectus supplement will be made without disclosure in Australia under Chapter 6D.2 of the Corporations Act, the offer of those securities for resale in Australia within 12 months may, under section 707 of the Corporations Act, require disclosure to investors under Chapter 6D.2 if none of the exemptions in section 708 applies to that resale. By applying for the securities you undertake to us that you will not, for a period of 12 months from the date of issue of the securities, offer, transfer, assign or otherwise alienate those securities to investors in Australia except in circumstances where disclosure to investors is not required under Chapter 6D.2 of the Corporations Act or where a compliant disclosure document is prepared and lodged with ASIC.

Notice to prospective investors in the Dubai International Financial Centre (“DIFC”)

This prospectus supplement and the accompanying prospectus relate to an Exempt Offer in accordance with the Markets Law, DIFC Law No. 1 of 2012, as amended. This prospectus supplement and the accompanying prospectus are intended for distribution only to persons of a type specified in the Markets Law, DIFC Law No. 1 of 2012, as amended. It must not be delivered to, or relied on by, any other person. The Dubai Financial Services Authority (DFSA) has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus supplement nor taken steps to verify the information set forth herein and has no responsibility for this prospectus supplement and the accompanying prospectus. The securities to which this prospectus supplement and the accompanying prospectus relate may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the securities offered should conduct their own due diligence on the securities. If you do not understand the contents of this prospectus supplement and the accompanying prospectus, you should consult an authorized financial advisor.

In relation to its use in the DIFC, this prospectus supplement and the accompanying prospectus are strictly private and confidential and are being distributed to a limited number of investors and must not be provided to any person other than the original recipient, and may not be reproduced or used for any other purpose. The interests in the securities may not be offered or sold directly or indirectly to the public in the DIFC.

Notice to Prospective Investors in the United Arab Emirates

The securities have not been, and are not being, publicly offered, sold, promoted or advertised in the United Arab Emirates (including the Dubai International Financial Centre) other than in compliance with the laws of the United Arab Emirates (and the Dubai International Financial Centre) governing the issue, offering and sale of securities. Further, this prospectus supplement does not constitute a public offer of securities in the United Arab Emirates (including the Dubai International Financial Centre) and is not intended to be a public offer. This prospectus supplement has not been approved by or filed with the Central Bank of the United Arab Emirates, the Securities and Commodities Authority or the Dubai Financial Services Authority.

Notice to Prospective Investors in Bermuda

Securities may be offered or sold in Bermuda only in compliance with the provisions of the Investment Business Act of 2003 of Bermuda which regulates the sale of securities in Bermuda. Additionally, non-Bermudian persons (including companies) may not carry on or engage in any trade or business in Bermuda unless such persons are permitted to do so under applicable Bermuda legislation.

Notice to Prospective Investors in the British Virgin Islands

The securities are not being, and may not be offered to the public or to any person in the British Virgin Islands for purchase or subscription by or on behalf of the Issuer. The securities may be offered to companies incorporated under the BVI Business Companies Act, 2004 (British Virgin Islands), (“BVI Companies”), but only where the offer will be made to, and received by, the relevant BVI Company entirely outside of the British Virgin Islands.

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Notice to Prospective Investors in South Africa

Due to restrictions under the securities laws of South Africa, no “offer to the public” (as such term is defined in the South African Companies Act, No. 71 of 2008 (as amended or re-enacted) (the “South African Companies Act”))is being made in connection with the issue of the securities in South Africa. Accordingly, this document does not, nor is it intended to, constitute a “registered prospectus” (as that term is defined in the South African Companies Act) prepared and registered under the South African Companies Act and has not been approved by, and/or filed with, the South African Companies and Intellectual Property Commission or any other regulatory authority in South Africa. The securities are not offered, and the offer shall not be transferred, sold, renounced or delivered, in South Africa or to a person with an address in South Africa, unless one or other of the following exemptions stipulated in section 96 (1) applies:

Section 96 (1) (a)

The offer, transfer, sale, renunciation or delivery is to:

(i) persons whose ordinary business, or part of whose ordinary business, is to deal in securities, as principal or agent;

(ii) the South African Public Investment Corporation;

(iii) persons or entities regulated by the Reserve Bank of South Africa;

(iv) authorised financial service providers under South African law;

(v) financial institutions recognised as such under South African law;

(vi) a wholly-owned subsidiary of any person or entity contemplated in (c), (d) or (e), acting as agent in the capacity of an authorised portfolio manager for a pension fund, or as manager for a collective investment scheme (in each case duly registered as such under South African law); or

(vii) any combination of the person in (i) to (vi); or

Section 96 (1) (b)

The total contemplated acquisition cost of the securities, for any single addressee acting as principal is equal to or greater than ZAR1,000,000 or such higher amount as may be promulgated by notice in the Government Gazette of South Africa pursuant to section 96(2)(a) of the South African Companies Act.

Information made available in this prospectus supplement should not be considered as “advice” as defined in the South African Financial Advisory and Intermediary Services Act, 2002.

Notice to Prospective Investors in Canada

The securities 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 securities 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 (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.

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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.

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LEGAL MATTERS

Cooley LLP, Chicago, Illinois, will pass upon the validity of the securities offered by this prospectus and any supplement thereto. The underwriters are being represented in connection with this offering by Davis Polk  & Wardwell LLP, Redwood City, California.

EXPERTS

The financial statements of RAPT Therapeutics, Inc. appearing in RAPT Therapeutics, Inc.’s Annual Report (Form 10-K) for the year ended December 31, 2024 have been audited by Ernst & Young LLP, independent registered public accounting firm, as forth in their report thereon included therein, and incorporated herein by reference. Such financial statements are incorporated herein by reference in reliance upon the report of Ernst & Young LLP pertaining to such financial statements given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

This prospectus supplement is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth or incorporated by reference in the registration statement. Whenever a reference is made in this prospectus supplement to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus supplement for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at www.sec.gov. In addition, we maintain a website that contains information about us at www.rapt.com. Information contained on or accessible through our website is not a part of this prospectus supplement and is not incorporated by reference herein, and the inclusion of our website address in this prospectus supplement is an inactive textual reference only.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement. Information in this prospectus supplement supersedes information in the accompanying prospectus or incorporated by reference that we filed with the SEC prior to the date of this prospectus supplement, while information that we file later with the SEC will automatically update and supersede the information in this prospectus supplement and accompanying prospectus. We incorporate by reference into this prospectus supplement and accompanying prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-38997):

• our Annual Report on  Form 10-K for the fiscal year ended December 31, 2024, filed with the SEC on March 6, 2025;

• our definitive Proxy Statement on  Schedule 14A, filed with the SEC on April 14, 2025 (excluding those portions that are not incorporated by reference into our Annual Report on Form 10-K for the fiscal year ended December 31, 2024);

• our Quarterly Reports on Form 10-Q for the quarters ended  March  31, 2025 and June 30, 2025, filed with the SEC on May 8, 2025 and August 7, 2025, respectively;

• our Current Reports on Form 8-K filed with the SEC on  March 27, 2025, May 28, 2025, May  29, 2025, June  17, 2025 and October 20, 2025; and

• the description of our common stock set forth in our registration statement on  Form 8-A, filed with the SEC on July 22, 2019, including any amendment or report filed for the purpose of updating such description, including Exhibit 4.2 to our Annual Report on Form 10-K for the fiscal year ended December 31, 2020.

Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have “furnished” to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus.

We also incorporate by reference all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus supplement and accompanying prospectus and will become a part of this prospectus supplement and accompanying prospectus from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus supplement and accompanying prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

We will provide to each person, including any beneficial owner, to whom a prospectus supplement and accompanying prospectus is delivered, without charge upon written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus but not delivered with the prospectus supplement and accompanying prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to RAPT Therapeutics, Inc., Attn: Chief Financial Officer, 561 Eccles Avenue, South San Francisco, California 94080; telephone: (650) 489-9000.

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Prospectus

$450,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

From time to time, we may offer and sell up to an aggregate amount of $450,000,000 of any combination of the securities described in this prospectus, either individually or in combination with other securities. We may also offer common stock or preferred stock upon conversion of debt securities, common stock upon conversion of preferred stock, or common stock, preferred stock or debt securities upon the exercise of warrants.

We will provide the specific terms of these offerings and securities in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectuses may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectuses, as well as any documents incorporated by reference, before buying any of the securities being offered.

Our common stock is listed on the Nasdaq Global Market under the trading symbol “RAPT.” On August 9, 2023, the last reported sale price of our common stock was $24.05 per share. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the Nasdaq Global Market or other securities exchange of the securities covered by the applicable prospectus supplement.

We are an “emerging growth company” under the federal securities laws and are subject to reduced public company reporting requirements.

Investing in our securities involves a high degree of risk. Before making an investment decision, you should review carefully the risks and uncertainties described under the heading “Risk Factors” on page 8 of this prospectus and any similar section contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the documents that are incorporated by reference into this prospectus.

This prospectus may not be used to consummate a sale of securities unless accompanied by a prospectus supplement.

The securities may be sold by us directly to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. The supplements to this prospectus will provide the specific terms of the plan of distribution. If any agents, underwriters or dealers are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents, underwriters or dealers and any applicable fees, commissions, discounts and options to purchase additional securities will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is August 17, 2023.

Table of Contents

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS			1
PROSPECTUS SUMMARY			3
RISK FACTORS			8
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS			9
USE OF PROCEEDS			11
DESCRIPTION OF CAPITAL STOCK			12
DESCRIPTION OF DEBT SECURITIES			17
DESCRIPTION OF WARRANTS			24
LEGAL OWNERSHIP OF SECURITIES			26
PLAN OF DISTRIBUTION			29
LEGAL MATTERS			31
EXPERTS			31
WHERE YOU CAN FIND ADDITIONAL INFORMATION			31
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE			31

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we have filed with the Securities and Exchange Commission, or SEC, using a “shelf” registration process. Under this shelf registration statement, we may, from time to time, offer and sell, either individually or in combination, in one or more offerings, up to a total dollar amount of $450,000,000 of any combination of the securities described in this prospectus.

This prospectus provides you with a general description of the securities we may offer. Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the 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 and any related free writing prospectuses that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents that we have incorporated by reference into this prospectus. We urge you to read carefully this prospectus, any applicable prospectus supplement and any free writing prospectuses we have authorized for use in connection with a specific offering, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before buying any of the securities being offered.

This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.

We have not authorized any other person to provide you with any information or to make any representations other than those contained in, or incorporated by reference into, this prospectus, any related prospectus supplement and any free writing prospectuses prepared by or on behalf of us or to which we have referred you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. You should assume that the information appearing in this prospectus, any related prospectus supplement and the documents incorporated by reference into this prospectus, any related prospectus supplement and in any free writing prospectuses that we may authorize 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, any related prospectus supplement, the documents incorporated by reference into this prospectus, and any free writing prospectuses that we may authorize for use in connection with this offering, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus captioned “Where You Can Find Additional Information” and “Incorporation of Certain Information by Reference.”

We are not making an offer to sell or soliciting an offer to buy our securities in any jurisdiction in which an offer or solicitation is not authorized 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. We are offering to sell, and seeking offers to buy, our securities only in jurisdictions where offers and sales are permitted. The distribution of this prospectus and any related prospectus supplement or free writing prospectuses and the offering of our securities in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus and any related prospectus supplement or free writing prospectuses must inform themselves about, and observe any restrictions relating to, the offering of our securities and the distribution of this prospectus and any related prospectus supplement outside the United States. This prospectus and any related prospectus supplement or free writing prospectuses does 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 and any related prospectus supplement by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

We obtained the industry and market data in this prospectus, including the information incorporated by reference herein, from our own research as well as from industry and general publications, surveys and studies conducted

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by third parties. These data involve a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions and estimates of our future performance and the future performance of the industry in which we operate is necessarily subject to a high degree of uncertainty and risk due to a variety of factors, including those described in “Risk Factors” and elsewhere in this prospectus, any related prospectus supplement, documents incorporated by reference into this prospectus and any related or free writing prospectuses. These and other factors could cause results to differ materially from those expressed in the estimates made by the independent parties and by us.

This prospectus and any related prospectus supplement, including the information incorporated by reference into this prospectus and any related prospectus supplement, include trademarks, service marks and trade names owned by us or others. All trademarks, service marks and trade names included or incorporated by reference in this prospectus, any related prospectus supplement or any related free writing prospectuses are the property of their respective owners.

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PROSPECTUS SUMMARY

This summary highlights selected information contained elsewhere in this prospectus or incorporated by reference in this prospectus, and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectuses, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectuses, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.

References in this prospectus to “RAPT,” “the Company,” “we,” “us” and “our” refer to RAPT Therapeutics, Inc., a Delaware corporation, and its consolidated subsidiaries, if any, unless otherwise specified. When we refer to “you,” we mean the holders of common stock of the Company.

RAPT Therapeutics, Inc.

Overview

We are a clinical-stage immunology-based therapeutics company focused on discovering, developing and commercializing oral small molecule therapies for patients with significant unmet needs in inflammatory diseases and oncology. Utilizing our proprietary drug discovery and development engine, we are developing highly selective small molecules designed to modulate the critical immune responses underlying these diseases. Our two lead inflammation drug candidates RPT193 and FLX475, each target C-C motif chemokine receptor 4, a drug target that potentially has broad applicability in inflammatory diseases and oncology.

In March 2023, we initiated a global 14-week randomized, double-blind, placebo-controlled Phase 2a clinical trial to evaluate the efficacy and safety of RPT193 as an oral, once-daily monotherapy in patients with moderate-to-severe asthma. The global multicenter Phase 2a trial will assess the efficacy and safety of RPT193 in adult patients with moderate-to-severe Type 2-high asthma whose disease is partially controlled by standard medications. The double-blind, placebo-controlled study will compare 400 mg once-daily RPT193 to placebo in approximately 100 patients randomized 1:1. The primary endpoint is the proportion of patients who experience a loss of asthma control.

Risks Associated with Our Business

Our business is subject to numerous risks. You should read these risks before you invest in our common stock. In particular, our risks include, but are not limited to, the following:

• We are a clinical stage biopharmaceutical company with a history of losses. We expect to continue to incur significant losses for the foreseeable future and may never achieve or maintain profitability.

• RPT193 and FLX475 are in clinical development, which may fail or suffer delays that materially and adversely affect their commercial viability. Clinical development includes a lengthy and expensive process with an uncertain outcome, and results of earlier studies and trials may not be predictive of future trial results. RPT193, FLX475 or other future drug candidates may not demonstrate the safety and efficacy necessary to support further clinical development or commercial viability.

• We may not be successful in our efforts to use and expand our proprietary drug discovery and development engine to build a pipeline of drug candidates, and as an organization we have no history of successfully developing drugs.

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• Even if regulatory approval is obtained for RPT193, FLX475 or any other potential drug candidate, the drug candidate we commercialize may not achieve market acceptance and we may not generate any revenue from the sale or licensing of our drug candidates.

• Undesirable side effects caused by RPT193, FLX475 or any other potential drug candidate could cause regulatory authorities to interrupt, delay or halt clinical trials and could result in the delay or denial of regulatory approval by the FDA or other regulatory authorities, which could compromise our ability to market and derive revenue from our drug candidates.

• We will need substantial additional funds to advance development of drug candidates and our drug discovery and development engine, and we cannot guarantee that we will have sufficient funds available in the future to develop and commercialize our current or potential future drug candidates.

• Because we may rely on third parties for manufacturing and supply of our drug candidates, some of which are sole source vendors, our supply may become limited or interrupted or may not be of satisfactory quantity or quality.

• If third parties on which we rely to conduct certain preclinical studies and clinical trials do not perform as contractually required, fail to satisfy regulatory or legal requirements or miss expected deadlines, our development program could be delayed with material and adverse impacts on our business and financial condition.

• We face intense competition from companies that have developed or may develop biologics and small molecule drugs for the treatment of inflammatory diseases and cancer. If these companies develop technologies or drug candidates more rapidly than we do, or if their technologies or drug candidates are more effective, our ability to develop and successfully commercialize drug candidates may be adversely affected.

• If any of our drug candidates is approved for marketing and commercialization in the future and we are unable to develop sales, marketing and distribution capabilities on our own or enter into agreements with third parties to perform these functions on acceptable terms, we will be unable to successfully commercialize any such future products.

• Our business could be materially and adversely affected in the future by effects of disease outbreaks, epidemics and pandemics, including the COVID-19 pandemic.

• If we are unable to obtain, maintain, enforce or defend intellectual property rights related to our technology and current or future drug candidates, or if our intellectual property rights are inadequate, we may not be able to compete effectively.

• Our stock price may be volatile. Raising additional capital and other future issuances of our common stock or rights to purchase common stock could result in additional dilution and could cause our stock price to fall.

• Our principal stockholders and management own a significant percentage of our stock and are able to exert significant control over matters subject to stockholder approval.

Corporate Information

RAPT Therapeutics, Inc., was incorporated under the laws of the State of Delaware in March 2015 under the name FLX Bio, Inc. In May 2019, we changed our name to RAPT Therapeutics, Inc. Our principal executive offices are located at 561 Eccles Avenue, South San Francisco, California 94080. The telephone number at our executive office is (650) 489-9000. Our corporate website address is www.rapt.com. We do not incorporate the information contained on, or accessible through, our website into this prospectus, and you should not consider it part of this prospectus. Our website address is included in this prospectus as an inactive textual reference only.

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The Securities We May Offer

We may offer shares of our common stock and preferred stock, various series of debt securities and/or warrants to purchase any of such securities, either individually or in combination, up to a total dollar amount of $450,000,000, from time to time under this prospectus, together with the applicable prospectus supplement and any related free writing prospectuses, at prices and on terms to be determined by market conditions at the time of any offering. We may also offer common stock, preferred stock and/or debt securities upon the exercise of warrants. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

• designation or classification;

• aggregate principal amount or aggregate offering price;

• maturity date, if applicable;

• original issue discount, if any;

• rates and times of payment of interest or dividends, if any;

• redemption, conversion, exercise, exchange or sinking fund terms, if any;

• conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange;

• ranking;

• restrictive covenants, if any;

• voting or other rights, if any; and

• material or special U.S. federal income tax considerations, if any.

The applicable prospectus supplement and any related free writing prospectuses that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents we have incorporated by reference. However, no prospectus supplement or free writing prospectuses will offer a security that is not registered and described in this prospectus at the time of the effectiveness of the registration statement of which this prospectus is a part.

THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

We may sell the securities directly to investors or to or through agents, underwriters or dealers. We and our agents, underwriters or dealers, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities to or through agents, underwriters or dealers, we will include in the applicable prospectus supplement:

• the names of those agents, underwriters or dealers;

• applicable fees, discounts and commissions to be paid to them;

• details regarding over-allotment options, if any; and

• the net proceeds to us.

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Common Stock. We may issue shares of our common stock from time to time. The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of stockholders. Subject to preferences that may be applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of legally available funds. Upon our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive or subscription rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to our common stock. In this prospectus, we have summarized certain general features of the common stock under “Description of Capital Stock — Common Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectuses that we may authorize to be provided to you) related to any common stock being offered.

Preferred Stock. We may issue shares of our preferred stock from time to time, in one or more series. Our board of directors will determine the designations, voting powers, preferences and rights of the preferred stock, as well as the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, preemptive rights, terms of redemption or repurchase, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of any series. Convertible preferred stock will be convertible into our common stock or exchangeable for other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

If we sell any series of preferred stock under this prospectus, we will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. In this prospectus, we have summarized certain general features of the preferred stock under “Description of Capital Stock — Preferred Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectuses that we may authorize to be provided to you) related to the series of preferred stock being offered, as well as the complete certificate of designation that contains the terms of the applicable series of preferred stock.

Debt Securities. We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other unsecured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible debt securities will be convertible into or exchangeable for our common stock or other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

Any debt securities issued under this prospectus will be issued under one or more documents called indentures, which are contracts between us and a national banking association or other eligible party, as trustee. In this prospectus, we have summarized certain general features of the debt securities under “Description of Debt Securities.” We urge you, however, to read the applicable prospectus supplement (and any free writing prospectuses that we may authorize to be provided to you) related to the series of debt securities being offered, as well as the complete indentures that contain the terms of the debt securities. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

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Warrants. We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or in combination with common stock, preferred stock and/or debt securities. In this prospectus, we have summarized certain general features of the warrants under “Description of Warrants.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectuses that we may authorize to be provided to you) related to the particular series of warrants being offered, as well as any warrant agreements and warrant certificates that contain the terms of the warrants. We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants.

Any warrants issued under this prospectus may be evidenced by warrant certificates. Warrants also may be issued under an applicable warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if applicable, in the prospectus supplement relating to the particular series of warrants being offered.

Use of Proceeds

Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital, capital expenditures and other general corporate purposes including research and development expenses, or for any other purpose we describe in the applicable prospectus supplement. See “Use of Proceeds” in this prospectus.

Nasdaq Global Market Listing

Our common stock is listed on the Nasdaq Global Market under the symbol “RAPT.” The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the Nasdaq Global Market or other securities exchange of the securities covered by the applicable prospectus supplement.

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RISK FACTORS

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectuses, and discussed under the section entitled “Risk Factors” contained in our most recent Annual Report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus, the documents incorporated by reference and any applicable prospectus supplement and free writing prospectuses that we may authorize for use in connection with this offering. The risks described in these documents are not the only ones we face, but those that we consider to be material. 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 common stock to decline, resulting in a loss of all or part of your investment. Please also read carefully the section below entitled “Special Note Regarding Forward-Looking Statements.”

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and any accompanying prospectus supplement, as well as the documents we have filed with the SEC that are incorporated by reference in this prospectus or any accompanying prospectus supplement contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, or the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:

• estimates of our total addressable market, future revenue, expenses, capital requirements and our needs for additional financing;

• the initiation, cost, timing, progress and results of research and development activities, preclinical studies and clinical trials with respect to RPT193, FLX475 and potential future drug candidates;

• our ability to identify, develop and commercialize drug candidates;

• our ability to advance RPT193, FLX475 or other future drug candidates into, and successfully complete, preclinical studies and clinical or field trials;

• our ability to obtain and maintain regulatory approval of RPT193, FLX475 or other future drug candidates, and any related restrictions, limitations and/or warnings in the label of an approved drug candidate;

• our ability to develop and expand our drug discovery and development engine;

• our ability to identify drug candidates using our drug discovery and development engine;

• our ability to obtain funding for our operations;

• our ability to contract with third-party suppliers and manufacturers and their ability to perform adequately under those arrangements;

• our ability to obtain and maintain intellectual property protection for our technology and any of our drug candidates;

• our ability to successfully commercialize any of our drug candidates;

• the rate and degree of market acceptance of any of our drug candidates;

• regulatory developments in the United States and international jurisdictions;

• potential liability lawsuits and penalties related to our technology, our drug candidates and our current and future relationships with third parties;

• our ability to attract and retain key scientific and management personnel;

• our ability to effectively manage the growth of our operations;

• our ability to compete effectively with existing competitors and new market entrants;

• our expectations regarding uses of proceeds from capital raising transactions;

• potential effects of extensive government regulation;

• our financial performance;

• our expectation regarding the time during which we will be an emerging growth company under the JOBS Act;

• the volatility of the trading price of our common stock; and

• other risks and uncertainties, including those listed under the caption “Risk Factors.”

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In some cases, you can identify forward-looking statements by terms such as “anticipates,” “believes,” “could,” “estimates,” “expects,” “may,” “plans,” “potential” “predicts,” “projects,” “should,” “will,” “would,” and similar expressions intended to identify forward-looking statements. These statements reflect our current views with respect to future events and are based on assumptions and are subject to risks and uncertainties. Given these assumptions, risks and uncertainties, you should not place undue reliance on these forward-looking statements. We discuss in greater detail many of these risks under the heading “Risk Factors” contained in the applicable prospectus supplement, in any free writing prospectuses we may authorize for use in connection with a specific offering, and in our most recent Annual Report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. You should read this prospectus, any applicable prospectus supplement, together with the documents we have filed with the SEC that are incorporated by reference and any free writing prospectuses that we may authorize for use in connection with a specific offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

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USE OF PROCEEDS

Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital, capital expenditures and other general corporate purposes, including research and development expenses, or for any other purpose we describe in the applicable prospectus supplement.

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DESCRIPTION OF CAPITAL STOCK

Our authorized capital stock consists of 500,000,000 shares of common stock, $0.0001 par value per share, and 50,000,000 shares of preferred stock, $0.0001 par value per share. A description of material terms and provisions of our amended and restated certificate of incorporation, or the Certificate of Incorporation, amended and restated bylaws, or the bylaws, and applicable provisions of the General Law of the State of Delaware, or the DGCL, affecting the rights of holders of our capital stock is set forth below. The description is intended as a summary, and is qualified in its entirety by reference to our Certificate of Incorporation, our bylaws and the DGCL.

Common Stock

Voting Rights. Each holder of common stock is entitled to one vote for each share of common stock held on all matters submitted to a vote of the stockholders, including the election of directors. The Certificate of Incorporation and bylaws do not provide for cumulative voting rights in connection with election of directors unless, at the time of such election, we are subject to Section 2115(b) of the California General Corporation Law. The affirmative vote of holders of 66 2/3% of the voting power of all of the then-outstanding shares of capital stock, voting as a single class, will be required to amend certain provisions of our Certificate of Incorporation, including provisions relating to amending our bylaws, and removal of directors.

Dividends. Subject to preferences that may be applicable to any then outstanding preferred stock, the holders of outstanding shares of common stock may receive dividends, if any, as may be declared from time to time by the board of directors out of legally available funds. We have never issued a dividend on shares of our common stock and we have no intention to do so in the future.

Liquidation. In the event we liquidate, dissolve or wind up, the assets legally available for distribution shall be distributed ratably to the holders of shares of common stock and preferred stock after payment of liabilities, subject to the satisfaction of any liquidation preference granted to the holders of any outstanding shares of preferred stock.

Rights and Preferences. Holders of common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

Fully Paid and Nonassessable. All outstanding shares of common stock are fully paid and nonassessable.

Preferred Stock

Our board of directors is authorized, subject to limitations prescribed by Delaware law, to issue up to 50,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each series and to fix the designation, powers, preferences and rights of the shares of each series and any of its qualifications, limitations or restrictions. Our board of directors can also increase or decrease the number of shares of any series, but not below the number of shares of that series then outstanding, without any further vote or action by the company’s stockholders. Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring, discouraging or preventing a change in control of RAPT and may adversely affect the market price of RAPT’s common stock and the voting and other rights of the holders of common stock.

Our board of directors will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the

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certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. We will describe in the applicable prospectus supplement the terms of the series of preferred stock being offered, including, to the extent applicable:

• the title and stated value;

• the number of shares we are offering;

• the liquidation preference per share;

• the purchase price;

• the dividend rate, period and payment date and method of calculation for dividends;

• whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

• the procedures for any auction and remarketing, if applicable;

• the provisions for a sinking fund, if applicable;

• the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

• any listing of the preferred stock on any securities exchange or market;

• whether the preferred stock will be convertible into our common stock, and, if applicable, the conversion price, or how it will be calculated, and the conversion period;

• whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange price, or how it will be calculated, and the exchange period;

• voting rights of the preferred stock;

• preemptive rights, if any;

• restrictions on transfer, sale or other assignment;

• whether interests in the preferred stock will be represented by depositary shares;

• a discussion of material United States federal income tax considerations applicable to the preferred stock;

• the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

• any limitations on the issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the preferred stock.

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Registration Rights

We are party to an amended and restated investor rights agreement that provides certain registration rights to certain holders of our common stock. The requisite holders of registrable securities pursuant to the registration rights agreement have waived their registration rights in connection with the filing of the registration statement of which this prospectus forms a part and any offering of securities pursuant to such registration statement.

Anti-Takeover Effects of Provisions of Our Certificate of Incorporation, Bylaws and Delaware Law

Certificate of incorporation and bylaws. Our Certificate of Incorporation and bylaws include a number of provisions that may deter or impede hostile takeovers or changes of control or management. These provisions include:

• Issuance of Undesignated Preferred Stock. Our board of directors has the authority, without further action by the stockholders, to issue up to 50,000,000 shares of undesignated preferred stock with rights and preferences, including voting rights, designated from time to time by our board of directors. The existence of authorized but unissued shares of preferred stock enables our board of directors to make it more difficult or to discourage an attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise.

• Board of Directors Vacancies. Our Certificate of Incorporation and bylaws authorize only our board of directors to fill vacant directorships. In addition, the number of directors constituting our board of directors may be set only by resolution adopted by a majority vote of our entire board of directors. These provisions prevent a stockholder from increasing the size of our board of directors and gaining control of our board of directors by filling the resulting vacancies with its own nominees.

• Stockholder Action; Special Meetings of Stockholders. Our Certificate of Incorporation provides that our stockholders may not take action by written consent, but may only take action at annual or special meetings of our stockholders. Stockholders will not be permitted to cumulate their votes for the election of directors unless required by applicable law. Our bylaws provide that only the chairman of our board of directors, chief executive officer or a majority of our board of directors may call special meetings of our stockholders.

• Classified Board: Our Certificate of Incorporation provides for a classified board of directors consisting of three classes of directors, with staggered three-year terms. Only one class of directors will be elected at each annual meeting of our stockholders, with the other classes continuing for the remainder of their respective three-year terms. This provision may have the effect of delaying a change in control of our board.

• Advance Notice Requirements for Stockholder Proposals and Director Nominations. Our bylaws provide advance notice procedures for stockholders seeking to bring business before our annual meeting of stockholders, or to nominate candidates for election as directors at our annual meeting of stockholders. Our bylaws also specify certain requirements as to the form and content of a stockholder’s notice. These provisions may make it more difficult for our stockholders to bring matters before our annual meeting of stockholders or to nominate directors at annual meetings of stockholders.

We designed these provisions to enhance the likelihood of continued stability in the composition of our board of directors and its policies, to discourage certain types of transactions that may involve an actual or threatened acquisition of us, and to reduce our vulnerability to an unsolicited acquisition proposal. We also designed these provisions to discourage certain tactics that may be used in proxy fights. However, these provisions could have the effect of discouraging others from making tender offers for our shares and, as a consequence, they may also reduce fluctuations in the market price of our shares that could result from actual or rumored takeover attempts.

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Section 203 of the Delaware General Corporation Law

We are subject to Section 203 of the DGCL, which prohibits a Delaware corporation from engaging in a business combination with any interested stockholder for a period of three years following the date the person became an interested stockholder, with the following exceptions:

• before such date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested holder;

• upon completion of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction began, excluding for purposes of determining the voting stock outstanding (but not the outstanding voting stock owned by the interested stockholder) those shares owned (a) by persons who are directors and also officers and (b) pursuant to employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; and

• on or after such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of the stockholders, and not by written consent, by the affirmative vote of at least 66 2/3% of the outstanding voting stock that is not owned by the interested stockholder.

In general, Section 203 of the DGCL defines business combination to include the following:

• any merger or consolidation involving the corporation and the interested stockholder;

• any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

• subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

• any transaction involving the corporation that has the effect of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; and

• the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits by or through the corporation.

Section 203 of the DGCL defines an “interested stockholder” as an entity or person who, together with the entity’s or person’s affiliates and associates, beneficially owns, or is an affiliate of the corporation and within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation. A Delaware corporation may “opt out” of these provisions with an express provision in its certificate of incorporation. We have not opted out of these provisions, which may as a result, discourage or prevent mergers or other takeover or change of control attempts of us.

Choice of Forum

Our Certificate of Incorporation provides that the Court of Chancery of the State of Delaware will be the exclusive forum for the following types of actions or proceedings under Delaware statutory or common law: (i) any derivative action or proceeding brought on our behalf; (ii) any action asserting a claim of breach of a fiduciary duty owed by any director, officer or other employee of our company to us or our stockholders; (iii) any action asserting a claim against us or any director or officer or other employee of our company arising pursuant to the General Corporation Law of the State of Delaware, our Certificate of Incorporation or bylaws; or (iv) any action asserting a claim against us or any director or officer or other employee of our company that is governed by the internal affairs doctrine. This provision would not apply to claims brought to enforce a duty or liability created by the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction. Our Certificate of Incorporation further provides that the federal district courts of the United States of America will be the exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act.

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Transfer Agent and Registrar

Our transfer agent and registrar for our common stock is Equinti Trust Company, LLC. The transfer agent for any series of preferred stock that we may offer under this prospectus will be named and described in the applicable prospectus supplement related to that series.

Listing on the Nasdaq Global Market

Our common stock is listed on the Nasdaq Global Market the symbol “RAPT.” The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the Nasdaq Global Market or any securities market or other exchange of the preferred stock covered by such prospectus supplement.

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DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

• the title of the series of debt securities;

• any limit upon the aggregate principal amount that may be issued;

• the maturity date or dates;

• the form of the debt securities of the series;

• the applicability of any guarantees;

• whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

• whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;

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• if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;

• the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

• our right, if any, to defer payment of interest and the maximum length of any such deferral period;

• if applicable, the date or dates after which, or the period or periods during which, and the price or prices at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

• the date or dates, if any, on which, and the price or prices at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

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

• any and all terms, if applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities and any other terms which may be advisable in connection with the marketing of debt securities of that series;

• whether the debt securities of the series shall be issued in whole or in part in the form of a global security or securities;

• the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities, and the depositary for such global security or securities;

• if applicable, the provisions relating to conversion or exchange of any debt securities of the series and the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders’ option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange;

• if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;

• additions to or changes in the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;

• additions to or changes in the events of default with respect to the securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such securities to be due and payable;

• additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;

• additions to or changes in the provisions relating to satisfaction and discharge of the indenture;

• additions to or changes in the provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture;

• the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars;

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• whether interest will be payable in cash or additional debt securities at our or the holders’ option and the terms and conditions upon which the election may be made;

• the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any, and principal amounts of the debt securities of the series to any holder that is not a “United States person” for federal tax purposes;

• any restrictions on transfer, sale or assignment of the debt securities of the series; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, any other additions or changes in the provisions of the indenture, and any terms that may be required by us or advisable under applicable laws or regulations.

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of our assets as an entirety or substantially as an entirety. However, any successor to or acquirer of such assets (other than a subsidiary of ours) must assume all of our obligations under the indenture or the debt securities, as appropriate.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

• if we fail to pay any installment of interest on any series of debt securities, as and when the same shall become due and payable, and such default continues for a period of 90 days; provided, however, that a valid extension of an interest payment period by us in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of interest for this purpose;

• if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when the same shall become due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series; provided, however, that a valid extension of the maturity of such debt securities in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of principal or premium, if any;

• if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive written notice of such failure, requiring the same to be remedied and stating that such is a notice of default thereunder, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

• if specified events of bankruptcy, insolvency or reorganization occur.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal

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amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. 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, provided that:

• the direction so given by the holder is not in conflict with any law or the applicable indenture; and

• subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:

• the holder has given written notice to the trustee of a continuing event of default with respect to that series;

• the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request,

• such holders have offered to the trustee indemnity satisfactory to it against the costs, expenses and liabilities to be incurred by the trustee in compliance with the request; and

• the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

• to cure any ambiguity, defect or inconsistency in the indenture or in the debt securities of any series;

• to comply with the provisions described above under “Description of Debt Securities—Consolidation, Merger or Sale;”

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

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• to add to our covenants, restrictions, conditions or provisions such new covenants, restrictions, conditions or provisions for the benefit of the holders of all or any series of debt securities, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in the indenture;

• to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

• to make any change that does not adversely affect the interests of any holder of debt securities of any series in any material respect;

• to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under “Description of Debt Securities—General” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

• to evidence and provide for the acceptance of appointment under any indenture by a successor trustee; or

• to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act.

In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

• extending the fixed maturity of any debt securities of any series;

• reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of any debt securities; or

• reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

• provide for payment;

• register the transfer or exchange of debt securities of the series;

• replace stolen, lost or mutilated debt securities of the series;

• pay principal of and premium and interest on any debt securities of the series;

• maintain paying agencies;

• hold monies for payment in trust;

• recover excess money held by the trustee;

• compensate and indemnify the trustee; and

• appoint any successor trustee.

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In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or DTC, or another depositary named by us and identified in the applicable prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating to any book-entry securities will be set forth in the applicable prospectus supplement.

At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

• issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

• register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

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Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the internal laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

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DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplements and in any related free writing prospectuses that we may authorize to be distributed to you, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may consist of warrants to purchase common stock, preferred stock or debt securities and be issued in one or more series. Warrants may be offered independently or in combination with common stock, preferred stock or debt securities offered by any prospectus supplement. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.

We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that describe the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectuses, and the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including:

• the offering price and aggregate number of warrants offered;

• the currency for which the warrants may be purchased;

• if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

• in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

• in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

• the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

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

• any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

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

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• the manner in which the warrant agreements and warrants may be modified;

• a discussion of any material or special U.S. federal income tax considerations of holding or exercising the warrants;

• the terms of the securities issuable upon exercise of the warrants; and

• any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:

• in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture; or

• in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or, payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the close of business on the expiration date set forth in the prospectus supplement relating to the warrants offered thereby. After the close of business on the expiration date, unexercised warrants will become void.

Upon receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants.

Governing Law

Unless we otherwise specify in the applicable prospectus supplement, the warrants and any warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

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LEGAL OWNERSHIP OF SECURITIES

We may issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

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For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

• how it handles securities payments and notices;

• whether it imposes fees or charges;

• how it would handle a request for the holders’ consent, if ever required;

• whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

• how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

• if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under the section entitled “Special Situations When a Global Security Will Be Terminated” in this prospectus. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

The rights of an indirect holder relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We

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do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

• an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

• an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

• an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

• an investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

• the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security;

• we and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security, nor do we or any applicable trustee supervise the depositary in any way;

• the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

• financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following special situations occur:

• if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

• if we notify any applicable trustee that we wish to terminate that global security; or

• if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

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PLAN OF DISTRIBUTION

We may sell the securities from time to time pursuant to underwritten public offerings, “at the market” offerings as defined in Rule 415 under the Securities Act at negotiated prices, direct sales to the public, negotiated transactions, block trades or a combination of these methods. We may sell the securities to or through one or more underwriters or dealers (acting as principal or agent), through agents, or directly to one or more purchasers. We may distribute the securities from time to time in one or more transactions:

• at a fixed price or prices, which may be changed from time to time;

• at market prices prevailing at the time of sale;

• at prices related to such prevailing market prices; or

• at negotiated prices.

A prospectus supplement or supplements (and any related free writing prospectuses that we may authorize to be provided to you) will describe the terms of the offering of the securities by us, including, to the extent applicable:

• the name or names of the underwriters, if any;

• the amounts of securities underwritten or purchased by each of them;

• the purchase price of the securities or other consideration therefor, and the proceeds, if any, we will receive from the sale;

• any options under which underwriters may purchase additional securities from us;

• any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

• any public offering price;

• any discounts or concessions allowed or reallowed or paid to dealers; and

• any securities exchange or market on which the securities may be listed.

Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement. Dealers and agents participating in the distribution of the securities may be deemed to be underwriters, and compensation received by them on resale of the securities may be deemed to be underwriting discounts. If such dealers or agents were deemed to be underwriters, they may be subject to statutory liabilities under the Securities Act.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the applicable prospectus supplement, other than securities covered by any option to purchase additional securities. If a dealer is used in the sale of securities, we or an underwriter 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. To the extent required, we will set forth in the prospectus supplement the name of the dealer and the terms of the transaction. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.

We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions we will pay the agent in the

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prospectus supplement. Unless the applicable prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

We may authorize agents, underwriters or dealers to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents, underwriters and dealers with indemnification against civil liabilities, including liabilities under the Securities Act, or contribution with respect to payments that the agents, underwriters or dealers may make with respect to these liabilities. Agents, underwriters and dealers, or their affiliates, may engage in transactions with, or perform services for, us in the ordinary course of business.

All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

Any underwriter may engage in over-allotment, stabilizing transactions, short-covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Over-allotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum price. Syndicate-covering or other short-covering transactions involve purchases of the securities, either through exercise of the over-allotment option or in the open market after the distribution is completed, to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

Any underwriters or agents that are qualified market makers on the Nasdaq Global Market may engage in passive market making transactions in the common stock on the Nasdaq Global Market in accordance with Regulation M under the Exchange Act, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and the applicable prospectus supplement.

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LEGAL MATTERS

Cooley LLP will pass upon the validity of the securities offered by this prospectus, and any supplement thereto, unless otherwise indicated in the applicable prospectus supplement. 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

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2022, as set forth in their report, which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. In addition, we maintain a website that contains information about us at www.rapt.com. The information found on, or otherwise accessible through our website is not incorporated by reference into, and does not form a part of, this prospectus or any accompanying prospectus supplement or any other document or report we file or furnish with the SEC.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to incorporate by reference information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-38997):

• our Annual Report on Form 10-K, for the year ended December 31, 2022, filed with the SEC on March 14, 2023;

• the information specifically incorporated by reference in our Annual Report on Form 10-K for the year ended December 31, 2022, from our Definitive Proxy Statement on Schedule 14A relating to our 2023 Annual Meeting of Stockholders, which was filed with the SEC on April 7, 2023;

• our Quarterly Report on Form 10-Q, for the quarter ended March 31, 2023, filed with the SEC on May 11, 2023, and our Quarterly Report on Form 10-Q, for the quarter ended June  30, 2023, filed with the SEC on August 11, 2023;

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• our Current Reports on Form 8-K filed with the SEC on January  9, 2023, March  14, 2023, and May 26, 2023; and

• the description of our common stock set forth in our registration statement on Form 8-A, filed with the SEC on July 22, 2019, including any amendment or report filed for the purpose of updating such description.

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including those made after the date of the initial filing of the registration statement of which this prospectus is a part and prior to effectiveness of such registration statement, until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus, which will become a part of this prospectus from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later-filed document modify or replace such earlier statements. We will furnish without charge to each person, including any beneficial owner, to whom a prospectus is delivered, upon written or oral request, a copy of any or all of the documents incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to:

RAPT Therapeutics, Inc.

Attn: Chief Financial Officer

561 Eccles Avenue

South San Francisco, California 94080

(650) 489-9000 

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Shares of Common Stock

PRELIMINARY PROSPECTUS SUPPLEMENT

Joint Bookrunning Managers

Leerink Partners

TD Cowen

Guggenheim Securities

Wells Fargo Securities

LifeSci Capital

Lead Managers

H.C. Wainwright & Co.

Clear Street

October , 2025