Atrium CSO has 8,320 shares withheld for taxes

Atrium Therapeutics’ chief strategy officer had 8,320 shares withheld to cover taxes on RSU vesting, leaving 38,340 shares held directly.

Rhea-AI Filing Summary

Atrium Therapeutics, Inc. (RNA) reported that Chief Strategy Officer Rocio Martin Hoyos had 8,320 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations upon the vesting of restricted stock units. The shares were treated as a disposition at a reference price of $8.95 per share, and Hoyos now holds 38,340 common shares directly. No Rule 10b5-1 trading plan is reported for this transaction.

Insider Trade Summary

Tax Withholding: 8,320 shares

Tax Withholding 1 txn

Insider Hoyos Rocio Martin

Role Chief Strategy Officer

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock F1	8,320	$8.95	$74K

Holdings After Transaction: Common Stock — 38,340 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: 8,320 shares Reference price per share: $8.95 per share Shares held after transaction: 38,340 shares +2 more

5 metrics

Shares withheld for taxes 8,320 shares Common stock withheld on September 18, 2026 for tax withholding obligations

Reference price per share $8.95 per share Value used for the 8,320 shares withheld for tax purposes

Shares held after transaction 38,340 shares Common shares directly held by Rocio Martin Hoyos following the transaction

Tax-liability-related shares 8,320 shares Total shares reported as delivered or withheld for payment of tax liability

Transactions for tax liability 1 transaction One Form 4 transaction coded as payment of tax liability by delivering or withholding securities

Key Terms

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

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

Rule 10b5-1 trading plan regulatory

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

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

FAQ

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

What insider transaction did Atrium Therapeutics (RNA) disclose for Rocio Martin Hoyos?

The company disclosed that Chief Strategy Officer Rocio Martin Hoyos had 8,320 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations related to vesting restricted stock units.

Was the Atrium Therapeutics (RNA) insider transaction a market sale or tax withholding?

It was reported as a payment of tax liability by delivering or withholding securities, with 8,320 shares of common stock withheld in connection with the vesting of restricted stock units, not an open-market sale.

What price per share was used for the tax-withholding shares at Atrium Therapeutics (RNA)?

The 8,320 shares withheld for tax purposes were valued at a reference price of $8.95 per share, according to the Form 4 disclosure for Chief Strategy Officer Rocio Martin Hoyos.

How many Atrium Therapeutics (RNA) shares does Rocio Martin Hoyos hold after the transaction?

After the tax-withholding disposition of 8,320 shares, Chief Strategy Officer Rocio Martin Hoyos directly holds 38,340 shares of Atrium Therapeutics common stock.

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

No. The filing indicates that no Rule 10b5-1 trading plan applies to this transaction; the box affirming such a plan is not checked.

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

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Available on EDGAR 09/22/2026 - 04:17 PM Accepted by SEC EDGAR 09/22/2026 - 04:15 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^*

Hoyos Rocio Martin

(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 Strategy 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)		8,320	D	$8.95	38,340	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)