BlackRock reports 5.2% stake in Atrium Therapeutics

BlackRock, Inc. files a Schedule 13G reporting beneficial ownership of 892,387 shares of Atrium Therapeutics, Inc. common stock, representing 5.2% of the class as reported.

Rhea-AI Filing Summary

BlackRock, Inc. files a Schedule 13G reporting beneficial ownership of 892,387 shares of Atrium Therapeutics, Inc. common stock, representing 5.2% of the class as reported. The filing lists sole voting power for 880,175 shares and sole dispositive power for 892,387 shares. The cover date shown is 03/31/2026 and the Schedule is signed on 04/27/2026. The filing states the holdings reflect securities held by certain Reporting Business Units of BlackRock and notes various persons may have rights to dividends or sale proceeds.

Insights

Institutional Ownership Analyst

Large passive investor reports a 5.2% stake in Atrium Therapeutics.

The filing shows 892,387 shares beneficially owned with 880,175 shares of sole voting power, indicating centralized voting authority within BlackRock's reporting units. This profile is typical for investment managers filing under Schedule 13G when holdings are passive.

Cash‑flow treatment and trading intentions are not stated; subsequent filings may disclose changes in position.

Securities Compliance Attorney

Schedule 13G disclosure aligns with passive investor reporting requirements.

The submission references SEC Release No. 34-39538 and attributes holdings to certain Reporting Business Units of BlackRock, consistent with aggregated reporting guidance. It includes required voting and dispositive power counts and an Exhibit listing for Item 7.

The signature date is 04/27/2026, which completes the filing formalities for the period ended 03/31/2026.

Key Figures

Beneficially owned: 892,387 shares Percent of class: 5.2% Sole voting power: 880,175 shares +3 more

6 metrics

Beneficially owned 892,387 shares Schedule 13G cover date <date>03/31/2026</date>

Percent of class 5.2% Reported in Item 4(b) of the Schedule 13G

Sole voting power 880,175 shares Item 4(c)(i) voting power reported

Sole dispositive power 892,387 shares Item 4(c)(iii) dispositive power reported

CUSIP 04965N104 Identifies Atrium Therapeutics common stock

Signature date 04/27/2026 Schedule signed by Spencer Fleming, Managing Director

Key Terms

Schedule 13G, beneficially owned, sole dispositive power

3 terms

Schedule 13G regulatory

"In accordance with SEC Release No. 34-39538 (January 12, 1998), this reflects"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

beneficially owned financial

"Amount beneficially owned: 892387"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole dispositive power regulatory

"Sole power to dispose or to direct the disposition of: 892387"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What stake does BlackRock hold in Atrium Therapeutics (RNA)?

BlackRock reports beneficial ownership of 892,387 shares, equal to 5.2% of Atrium Therapeutics' common stock. The Schedule 13G shows sole voting power on 880,175 shares and sole dispositive power on 892,387 shares.

As of what date does the Schedule 13G report BlackRock's holdings?

The ownership is reported with a cover date of 03/31/2026 and the Schedule is signed on 04/27/2026. Those dates anchor the reported beneficial ownership figures in the filing.

Does the filing say BlackRock controls voting or disposition of the shares?

Yes. The filing shows sole voting power for 880,175 shares and sole dispositive power for 892,387 shares, indicating BlackRock's reporting units hold direct authority to vote and dispose of those shares.

Are BlackRock's holdings described as passive or active in this filing?

The Schedule 13G presentation and the Release citation indicate holdings are reported by certain Reporting Business Units, consistent with passive/aggregated reporting. The filing does not state active control or intent to influence management.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 04/27/2026 - 04:12 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Atrium Therapeutics, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

04965N104

(CUSIP Number)

03/31/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 04965N104

1

Names of Reporting Persons

BlackRock, Inc.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 880,175.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 892,387.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

892,387.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

5.2 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Atrium Therapeutics, Inc.
(b)	Address of issuer's principal executive offices: 10578 Science Center Drive, Suite 125 San Diego CA 92121
Item 2.
(a)	Name of person filing: BlackRock, Inc. In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by certain business units (collectively, the "Reporting Business Units") of BlackRock, Inc. and its subsidiaries and affiliates. It does not include securities, if any, beneficially owned by other business units whose beneficial ownership of securities are disaggregated from that of the Reporting Business Units in accordance with such release.
(b)	Address or principal business office or, if none, residence: BlackRock, Inc., 50 Hudson Yards New York, NY 10001
(c)	Citizenship: See Item 4 of Cover Page
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 04965N104
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 892387
(b)	Percent of class: 5.2 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 880175
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 892387
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Various persons have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of the common stock of Atrium Therapeutics, Inc.. No one person's interest in the common stock of Atrium Therapeutics, Inc. is more than five percent of the total outstanding common shares.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. See Exhibit 99
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

BlackRock, Inc.

Signature:	Spencer Fleming
Name/Title:	Managing Director
Date:	04/27/2026

Exhibit Information

Exhibit 24: Power of Attorney Exhibit 99: Item 7