BlackRock reports 6.6% stake in Atrium Therapeutics

BlackRock, Inc. reports beneficial ownership of common stock of Atrium Therapeutics, Inc. in this amended ownership filing.

Rhea-AI Filing Summary

BlackRock, Inc. reports beneficial ownership of common stock of Atrium Therapeutics, Inc. in this amended ownership filing. BlackRock reports beneficial ownership of 1,135,757 shares of common stock, representing 6.6% of the class.

BlackRock has sole voting power over 1,119,668 shares and sole dispositive power over all 1,135,757 shares, with no shared voting or dispositive power. Various underlying clients have rights to dividends and sale proceeds, but no single client holds more than five percent of Atrium Therapeutics’ outstanding common shares.

Key Figures

Beneficially owned shares: 1,135,757 shares Percent of class: 6.6% Sole voting power: 1,119,668 shares +3 more

6 metrics

Beneficially owned shares 1,135,757 shares Common stock of Atrium Therapeutics reported as beneficially owned by BlackRock

Percent of class 6.6% Portion of Atrium Therapeutics common stock class beneficially owned by BlackRock

Sole voting power 1,119,668 shares Shares of Atrium Therapeutics over which BlackRock has sole voting power

Sole dispositive power 1,135,757 shares Shares of Atrium Therapeutics over which BlackRock has sole dispositive power

Form date 06/30/2026 Date associated with the Schedule 13G/A reporting BlackRock’s ownership

Signature date 07/27/2026 Date on which Managing Director Spencer Fleming signed the report

Key Terms

beneficially owned, sole voting power, sole dispositive power, percent of class, +2 more

6 terms

beneficially owned financial

"this reflects the securities beneficially owned, or deemed to be beneficially owned"

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 voting power financial

"Sole Voting Power 1,119,668.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"Sole Dispositive Power 1,135,757.00"

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.

percent of class financial

"Percent of class: 6.6 %"

Percent of class is the portion of a specific category of securities—such as a company’s common shares, preferred shares, or a bond series—that takes part in or approves a corporate action (vote, consent, tender, etc.). Investors watch this number because it reveals how much support or opposition exists within that particular shareholder group; like counting how many members of a club back a proposal, it can determine whether a plan passes or how influence is distributed.

parent holding company financial

"If a parent holding company has filed this schedule"

Power of Attorney regulatory

"Exhibit 24: Power of Attorney"

A power of attorney is a legal document that allows one person to make decisions and act on behalf of another person, often in financial or legal matters. It’s like giving someone a trusted helper or agent the authority to handle important tasks if you are unable to do so yourself. This matters to investors because it can impact how their assets are managed or transferred if they become unable to oversee their affairs.

FAQ

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

What percentage of Atrium Therapeutics (RNA) does BlackRock currently report owning?

BlackRock reports beneficial ownership of 6.6% of Atrium Therapeutics’ common stock. This corresponds to 1,135,757 shares as disclosed in the Schedule 13G/A, giving BlackRock a significant institutional position above the five percent reporting threshold.

How many Atrium Therapeutics (RNA) shares does BlackRock beneficially own?

BlackRock beneficially owns 1,135,757 shares of Atrium Therapeutics common stock. These holdings represent 6.6% of the outstanding class and are reported as being under BlackRock’s control through certain of its business units.

What voting power does BlackRock have over Atrium Therapeutics (RNA) shares?

BlackRock has sole voting power over 1,119,668 Atrium Therapeutics shares. It reports no shared voting power, meaning decisions on voting these shares are controlled solely by BlackRock’s reporting business units, subject to client arrangements.

What dispositive power does BlackRock report for its Atrium Therapeutics (RNA) position?

BlackRock reports sole dispositive power over 1,135,757 Atrium Therapeutics shares and no shared dispositive power. Sole dispositive power means BlackRock can direct the disposition of these shares, such as sales, on behalf of its clients.

Do any single BlackRock clients hold over 5% of Atrium Therapeutics (RNA)?

No. The filing states that various persons have rights to dividends or sale proceeds for Atrium shares, but that no one person’s interest exceeds five percent of the total outstanding common shares of Atrium Therapeutics.

Who signed the BlackRock ownership report for Atrium Therapeutics (RNA)?

The ownership report is signed by Spencer Fleming, a Managing Director at BlackRock. The signature confirms the disclosure of BlackRock’s beneficial ownership and related powers over Atrium Therapeutics common stock.

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

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Available on EDGAR 07/27/2026 - 04:26 PM Accepted by SEC EDGAR 07/27/2026 - 04:25 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Atrium Therapeutics, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

04965N104

(CUSIP Number)

06/30/2026

(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 1,119,668.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,135,757.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,135,757.00

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)

6.6 %

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 No.: 04965N104
Item 4.	Ownership
(a)	Amount beneficially owned: 1135757
(b)	Percent of class: 6.6 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1119668
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1135757
	(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:	07/27/2026

Exhibit Information

Exhibit 24: Power of Attorney Exhibit 99: Item 7