Atrium Therapeutics director has 22,812 shares withheld

Atrium Therapeutics director reported shares withheld for taxes on RSU vesting, not an open-market trade.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) director Michael W. Flanagan reported a Form 4 reflecting the withholding of 22,812 shares of Common Stock on September 18, 2026 to satisfy tax withholding obligations arising from the vesting of restricted stock units. After this tax-withholding disposition, he holds 31,974 shares of Common Stock directly.

Insider Trade Summary

Tax Withholding: 22,812 shares

Tax Withholding 1 txn

Insider Flanagan W. Michael

Role Director

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	22,812	$8.95	$204K

Holdings After Transaction: Common Stock — 31,974 shares (Direct)

Footnotes (1)

1. F1. Represents shares withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting of restricted stock units.

Key Figures

Shares withheld for taxes: 22,812 shares Price per share: $8.95 per share Shares held after transaction: 31,974 shares

3 metrics

Shares withheld for taxes 22,812 shares Shares of Common Stock withheld on September 18, 2026 for tax withholding obligations on RSU vesting

Price per share $8.95 per share Value used for the tax-withholding disposition of 22,812 shares

Shares held after transaction 31,974 shares Common Stock directly owned by Michael W. Flanagan following the tax-withholding transaction

Key Terms

restricted stock units, tax withholding obligations, Common Stock

3 terms

restricted stock units financial

"in connection with the vesting of restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

tax withholding obligations financial

"to satisfy tax withholding obligations in connection with the vesting"

Common Stock financial

"Represents shares of Common Stock withheld by the Issuer"

Common stock represents ownership shares in a company, giving investors a stake in its success and a say in important decisions through voting rights. It is the most common type of stock traded on markets and can provide income through dividends, as well as potential for value growth. For investors, holding common stock means sharing in the company’s profits and risks.

FAQ

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

What insider transaction did Atrium Therapeutics (RNA) disclose in this Form 4?

The filing reports that 22,812 shares of Atrium Therapeutics Common Stock were withheld on September 18, 2026 to satisfy tax withholding obligations related to vesting restricted stock units, rather than being sold in an open-market transaction.

Who is the insider involved in this Atrium Therapeutics (RNA) Form 4 filing?

The insider is Michael W. Flanagan, who is identified as a director of Atrium Therapeutics, Inc. He reported a tax-withholding disposition of shares connected to restricted stock unit vesting.

How many Atrium Therapeutics (RNA) shares were withheld and at what price?

A total of 22,812 shares of Atrium Therapeutics Common Stock were withheld at a price of $8.95 per share in connection with satisfying tax withholding obligations on the vesting restricted stock units.

How many Atrium Therapeutics (RNA) shares does the director hold after this transaction?

Following the tax-withholding disposition, Michael W. Flanagan holds 31,974 shares of Atrium Therapeutics Common Stock directly, as reported in the Form 4 filing.

Was this Atrium Therapeutics (RNA) insider transaction part of a Rule 10b5-1 trading plan?

No. The filing indicates the Rule 10b5-1 checkbox is not marked, and the footnote describes the transaction as shares withheld to cover tax withholding obligations on restricted stock unit vesting.

Does this Atrium Therapeutics (RNA) Form 4 reflect an open-market sale or purchase?

No. The transaction is coded as F and described as payment of tax liability by delivering or withholding securities. It represents shares withheld for taxes, not an open-market sale or purchase.

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

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Available on EDGAR 09/22/2026 - 04:21 PM Accepted by SEC EDGAR 09/22/2026 - 04:20 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Flanagan W. Michael

(Last) (First) (Middle)

C/O ATRIUM THERAPEUTICS, INC.

10578 SCIENCE CENTER DRIVE, SUITE 125

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Atrium Therapeutics, Inc. [ RNA ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/18/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	09/18/2026		F(1)		22,812	D	$8.95	31,974	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Represents shares withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting of restricted stock units.

	/s/ Brendan Winslow, Attorney-in-Fact	09/22/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)