Atrium CFO has 6,742 shares withheld for taxes

Atrium Therapeutics’ CFO had shares withheld to cover RSU tax obligations, reducing his directly held position.

Available on EDGAR 09/22/2026 - 04:18 PM EDT Accepted by SEC EDGAR 09/22/2026 - 04:17 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that Chief Financial Officer Brendan R. Winslow had 6,742 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations upon vesting of restricted stock units. The shares were treated as a disposition and his directly held stake is now 36,859 shares. No Rule 10b5-1 trading plan is reported.

Insider Trade Summary

Tax Withholding: 6,742 shares

Tax Withholding 1 txn

Insider Winslow Brendan R.

Role Chief Financial Officer

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	6,742	$8.95	$60K

Holdings After Transaction: Common Stock — 36,859 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: 6,742 shares Price per share used for withholding: $8.95 per share Shares held after transaction: 36,859 shares

3 metrics

Shares withheld for taxes 6,742 shares Common stock withheld on September 18, 2026 to satisfy tax withholding obligations on RSU vesting

Price per share used for withholding $8.95 per share Value applied to the 6,742 common shares withheld for tax purposes

Shares held after transaction 36,859 shares Common shares of Atrium Therapeutics, Inc. directly held by the CFO after the withholding

Key Terms

restricted stock units, tax withholding obligations, withheld by the Issuer

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"

withheld by the Issuer financial

"Represents shares withheld by the Issuer to satisfy tax"

FAQ

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

What insider transaction did RNA’s CFO report on September 18, 2026?

Brendan R. Winslow, CFO of Atrium Therapeutics (RNA), reported that 6,742 common shares were withheld on September 18, 2026 to satisfy tax withholding obligations related to the vesting of restricted stock units.

Was the RNA insider transaction a market sale of shares?

No. The filing states the 6,742 shares represent shares withheld by the issuer to satisfy tax withholding obligations in connection with the vesting of restricted stock units, rather than an open-market sale.

What price per share was used for the RNA CFO’s tax withholding transaction?

The shares withheld from the RNA CFO for tax purposes used a price of $8.95 per share for the 6,742 common shares withheld on September 18, 2026.

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

Following the tax withholding transaction, Chief Financial Officer Brendan R. Winslow directly holds 36,859 shares of Atrium Therapeutics, Inc. common stock, as reported in the Form 4.

Was the RNA CFO’s September 2026 transaction under a Rule 10b5-1 plan?

No. The Form 4 indicates that no Rule 10b5-1 trading plan is affirmatively reported for the September 18, 2026 tax withholding transaction by the CFO of Atrium Therapeutics.

What type of equity award was involved in the RNA CFO’s Form 4?

The footnote explains that the withheld shares related to the vesting of restricted stock units of Atrium Therapeutics, Inc., with 6,742 common shares withheld to cover associated tax obligations.

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

Form 4 Insider Transactions: What Each Field Means →

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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^*

Winslow Brendan R.

(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)

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

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)		6,742	D	$8.95	36,859	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	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)