Atrium Therapeutics officer has 2,375 shares withheld

Atrium Therapeutics reported a routine tax-withholding share disposition tied to RSU vesting by its Chief Corporate Affairs Officer.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that Chief Corporate Affairs Officer Stephanie Kenney had 2,375 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations arising from vesting of restricted stock units. After this tax-withholding disposition, she directly holds 33,085 shares of common stock. No Rule 10b5-1 plan is reported.

Insider Trade Summary

Tax Withholding: 2,375 shares

Tax Withholding 1 txn

Insider Kenney Stephanie

Role See Remarks

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	2,375	$8.95	$21K

Holdings After Transaction: Common Stock — 33,085 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 disposed for tax withholding: 2,375 shares Price per share for tax-withholding shares: $8.95 per share Shares held after transaction: 33,085 shares +1 more

4 metrics

Shares disposed for tax withholding 2,375 shares Common stock withheld on September 18, 2026 to satisfy tax obligations from RSU vesting

Price per share for tax-withholding shares $8.95 per share Value applied to 2,375 shares withheld on September 18, 2026

Shares held after transaction 33,085 shares Direct holdings of common stock by Stephanie Kenney following the tax-withholding disposition

Tax-withholding disposition shares reported 2,375 shares Exercise-price-or-tax-liability category in transaction summary

Key Terms

restricted stock units, tax withholding obligations, Rule 10b5-1 plan

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

"shares withheld by the Issuer to satisfy tax withholding obligations"

Rule 10b5-1 plan regulatory

"No Rule 10b5-1 plan is reported for this transaction"

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

FAQ

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

What insider transaction did Atrium Therapeutics (RNA) report for Stephanie Kenney?

Atrium Therapeutics reported that Chief Corporate Affairs Officer Stephanie Kenney had 2,375 shares of common stock withheld on September 18, 2026 to cover tax withholding obligations from vesting restricted stock units.

How many Atrium Therapeutics (RNA) shares does Stephanie Kenney hold after this Form 4 transaction?

Following the reported tax-withholding share disposition, Stephanie Kenney directly holds 33,085 shares of Atrium Therapeutics common stock, as stated in the Form 4.

Was the September 18, 2026 RNA insider transaction a market sale or a tax withholding?

The September 18, 2026 transaction was a tax-withholding disposition. Shares were withheld by Atrium Therapeutics to satisfy tax obligations related to vesting restricted stock units, not a market sale.

What price per share is associated with the Atrium Therapeutics (RNA) tax-withholding shares?

The shares withheld for tax purposes are reported at $8.95 per share for the 2,375 shares of Atrium Therapeutics common stock involved in the September 18, 2026 transaction.

Was the Atrium Therapeutics (RNA) insider transaction made under a Rule 10b5-1 trading plan?

No. The filing’s Rule 10b5-1 checkbox is unchecked, and no footnote indicates a trading plan, so no Rule 10b5-1 plan is reported for this transaction.

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

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Available on EDGAR 09/22/2026 - 04:19 PM Accepted by SEC EDGAR 09/22/2026 - 04:18 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^*

Kenney Stephanie

(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)
	See Remarks

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)		2,375	D	$8.95	33,085	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.

Remarks:

Chief Corporate Affairs Officer

	/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)