Atrium Therapeutics director has 126K shares withheld

Director Sarah Boyce reported tax-related share withholding tied to RSU vesting, with 138,668 Atrium Therapeutics shares held afterward.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that director Sarah Boyce had 126,418 shares of Common Stock withheld on September 18, 2026 to satisfy tax withholding obligations arising from the vesting of restricted stock units. After this withholding transaction, she directly holds 138,668 shares of Atrium Therapeutics common stock. No Rule 10b5-1 trading plan is reported for this Form 4.

Insider Trade Summary

Tax Withholding: 126,418 shares

Tax Withholding 1 txn

Insider Boyce Sarah

Role Director

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	126,418	$8.95	$1.13M

Holdings After Transaction: Common Stock — 138,668 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: 126,418 shares Price per share: $8.95 per share Shares held after transaction: 138,668 shares +1 more

4 metrics

Shares withheld for taxes 126,418 shares Withheld on September 18, 2026 to satisfy tax withholding obligations on RSU vesting

Price per share $8.95 per share Associated with the 126,418 withheld shares reported in the Form 4

Shares held after transaction 138,668 shares Sarah Boyce’s direct holdings of Atrium Therapeutics Common Stock following the withholding

Transaction date September 18, 2026 Date of the tax withholding disposition of Common Stock

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) director Sarah Boyce report?

She reported that 126,418 shares of Atrium Therapeutics Common Stock were withheld on September 18, 2026 to cover tax withholding obligations related to the vesting of restricted stock units.

How many Atrium Therapeutics (RNA) shares does Sarah Boyce hold after the reported transaction?

After the tax withholding transaction, Sarah Boyce directly holds 138,668 shares of Atrium Therapeutics Common Stock, as reported in the Form 4 filing.

Was the Atrium Therapeutics (RNA) Form 4 transaction a market sale by Sarah Boyce?

No. The Form 4 states the 126,418 shares were withheld by the issuer to satisfy tax withholding obligations on vested restricted stock units, not sold in the open market.

What price per share is associated with Sarah Boyce’s Atrium Therapeutics (RNA) tax withholding transaction?

The filing reports a price of $8.95 per share for the 126,418 shares withheld to satisfy tax withholding obligations in connection with the vesting of restricted stock units.

Was Sarah Boyce’s Atrium Therapeutics (RNA) transaction under a Rule 10b5-1 trading plan?

No. The Form 4 indicates that no Rule 10b5-1 trading plan is reported in connection with this tax withholding transaction.

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

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Available on EDGAR 09/22/2026 - 04:20 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^*

Boyce Sarah

(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)		126,418	D	$8.95	138,668	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)