T. Rowe Price reports 1.55M RNA shares (10%)

T. Rowe Price Associates, Inc. reported beneficial ownership of 1,553,210 shares of Atrium Therapeutics common stock, representing 10.0% of the class as of 03/31/2026.

Rhea-AI Filing Summary

T. Rowe Price Associates, Inc. reported beneficial ownership of 1,553,210 shares of Atrium Therapeutics common stock, representing 10.0% of the class as of 03/31/2026. The filing lists sole voting power of 1,552,984 shares and sole dispositive power of 1,553,210 shares. The Schedule 13G is signed by a T. Rowe Price officer on 04/08/2026.

Insights

Institutional Ownership Analyst

T. Rowe Price holds a 10.0% passive stake in Atrium Therapeutics as disclosed on a Schedule 13G.

The filing shows 1,553,210 shares beneficially owned with sole voting power of 1,552,984 and sole dispositive power of 1,553,210 as of 03/31/2026. A Schedule 13G typically signals passive, not activist, ownership.

Watch subsequent filings for any shift to an active stance (Schedule 13D) or material changes in stake size; timing and further disclosures are governed by future filings.

Key Figures

Shares beneficially owned: 1,553,210 shares Percent of class: 10.0% Sole voting power: 1,552,984 shares +3 more

6 metrics

Shares beneficially owned 1,553,210 shares Amount beneficially owned as of 03/31/2026

Percent of class 10.0% Percent of common stock as of 03/31/2026

Sole voting power 1,552,984 shares Sole power to vote or direct the vote

Sole dispositive power 1,553,210 shares Sole power to dispose or direct disposition

Reporting form date 03/31/2026 Ownership reported as of this date

Signature date 04/08/2026 Filing signed by T. Rowe Price officer

Key Terms

Schedule 13G, beneficially owned, sole dispositive power, CUSIP

4 terms

Schedule 13G regulatory

"T. Rowe Price Associates, Inc. hereby declares and affirms"

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: 1553210"

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: 1553210"

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.

CUSIP technical

"CUSIP Number(s): 04965N104"

A CUSIP is a nine-character alphanumeric code that uniquely identifies a U.S. or Canadian financial security—such as a stock, bond, or fund share—like a Social Security number for an investment. It matters to investors because brokers, exchanges and record-keepers use the CUSIP to match trades, track ownership, settle transactions and pull accurate records, reducing errors and ensuring money and securities go to the right place.

FAQ

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

What stake does T. Rowe Price hold in Atrium Therapeutics (RNA)?

T. Rowe Price beneficially owns 1,553,210 shares, representing 10.0% of Atrium Therapeutics’ common stock as of 03/31/2026. The filing reports sole voting power of 1,552,984 shares and sole dispositive power of 1,553,210 shares.

Does the Schedule 13G indicate active control by T. Rowe Price?

No. A Schedule 13G generally indicates a passive investor position rather than an activist intent. The filing shows ownership and voting/dispositive powers but does not state any active control or plans.

What is the reporting date and signature date for this 13G filing for RNA?

Ownership is reported as of 03/31/2026, and the filing is signed by Ellen York, Vice President of T. Rowe Price, on 04/08/2026. Those dates anchor the disclosed position and signature certification.

How does the filing report voting and dispositive power for the shares?

The filing lists sole voting power of 1,552,984 shares and sole dispositive power of 1,553,210 shares. It reports no shared voting or dispositive power for this position.

Will this Schedule 13G filing change Atrium Therapeutics’ governance immediately?

No. The Schedule 13G discloses ownership but does not, by itself, change governance. Any governance impact would depend on future actions or additional filings such as a Schedule 13D or proxy-related disclosures.

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

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Accepted by SEC EDGAR 04/08/2026 - 03:25 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

T. Rowe Price Associates, 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

MARYLAND

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,552,984.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,553,210.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,553,210.00

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)

10.0 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: ATRIUM THERAPEUTICS INC
(b)	Address of issuer's principal executive offices: 3020 CALLAN ROAD, SAN DIEGO, CA, 92121
Item 2.
(a)	Name of person filing: T. Rowe Price Associates, Inc.
(b)	Address or principal business office or, if none, residence: 1307 Point Street, Baltimore, MD 21231
(c)	Citizenship: Maryland
(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: 1553210
(b)	Percent of class: 10.0 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1552984
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1553210
	(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.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
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. T. Rowe Price Associates, Inc. hereby declares and affirms that the filing of Schedule 13G shall not be construed as an admission that Price Associates is the beneficial owner of the securities referred to, which beneficial ownership is expressly denied.

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.

T. Rowe Price Associates, Inc.

Signature:	Ellen York
Name/Title:	Vice President
Date:	04/08/2026