Amentum (AMTM) officer details RSU vesting and 4,194-share tax withholding

Rhea-AI Filing Summary

Amentum Holdings, Inc. Chief Growth Officer reported the vesting of restricted stock units and related tax withholding. On December 17, 2025, 9,298 restricted stock units were converted into an equal number of AMTM common shares, reflecting a scheduled vesting event. On the same date, 4,194 shares of AMTM common stock were tendered to cover tax withholding obligations at a price of $28.67 per share. After these transactions, the officer directly beneficially owns 26,138 shares of AMTM common stock and no remaining restricted stock units from this award.

Insider Trade Summary

9,298 shares exercised/converted

Mixed 3 txns

Insider Mullen Sean Thomas

Role Chief Growth Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	9,298	$0.00	--
Exercise	Common Stock	9,298	$0.00	--
Tax Withholding	Common Stock	4,194	$28.67	$120K

Holdings After Transaction: Restricted Stock Units — 0 shares (Direct); Common Stock — 30,332 shares (Direct)

Footnotes (1)

1. Represents distribution of AMTM common stock upon vesting of restricted stock units. Represents number of shares of AMTM common stock tendered for tax withholding upon vesting of restricted stock units. Each restricted stock unit represents a contingent right to receive one share of AMTM common stock. The restricted stock units awarded vested on December 17, 2025.

Form 4 Insider Transactions: What Each Field Means →

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^*

Mullen Sean Thomas

(Last) (First) (Middle)

C/O AMENTUM HOLDINGS, INC.

4800 WESTFIELDS BOULEVARD, SUITE 400

(Street)

CHANTILLY VA 20151

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Amentum Holdings, Inc. [ AMTM ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
12/17/2025

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

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

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

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	12/17/2025		M		9,298	A	(1)	30,332	D
Common Stock	12/17/2025		F		4,194(2)	D	$28.67	26,138	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
Restricted Stock Units	(3)	12/17/2025		M(1)			9,298	(4)	(4)	Common Stock	9,298	$0	0	D

Explanation of Responses:

1. Represents distribution of AMTM common stock upon vesting of restricted stock units.

2. Represents number of shares of AMTM common stock tendered for tax withholding upon vesting of restricted stock units.

3. Each restricted stock unit represents a contingent right to receive one share of AMTM common stock.

4. The restricted stock units awarded vested on December 17, 2025.

Remarks:

	/s/ Mark Esposito, Attorney-in-Fact	12/19/2025
	** 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.

FAQ

What insider transaction did Amentum Holdings (AMTM) report on this Form 4?

The Chief Growth Officer reported the vesting of 9,298 restricted stock units into AMTM common stock and the related tax share withholding on December 17, 2025.

How many Amentum (AMTM) shares vested from restricted stock units?

A total of 9,298 restricted stock units vested, resulting in the distribution of 9,298 shares of AMTM common stock to the reporting officer.

How many Amentum (AMTM) shares were withheld for taxes in this transaction?

4,194 shares of AMTM common stock were tendered for tax withholding in connection with the vesting of the restricted stock units, at a price of $28.67 per share.

How many Amentum (AMTM) shares does the insider own after these transactions?

Following the reported transactions, the Chief Growth Officer directly beneficially owns 26,138 shares of AMTM common stock.

What does each restricted stock unit (RSU) represent for Amentum (AMTM)?

Each restricted stock unit reported represents a contingent right to receive one share of AMTM common stock upon vesting.

When did the Amentum (AMTM) restricted stock units vest?

The restricted stock units in this filing vested on December 17, 2025, triggering the distribution of AMTM common shares and related tax withholding.