Amentum (AMTM) COO logs RSU vesting and tax-withholding share disposition

Rhea-AI Filing Summary

Amentum Holdings, Inc. Chief Operating Officer Stephen A. Arnette reported equity award activity involving restricted stock units and common shares. On March 2, 2026, 2,808 restricted stock units were converted into 2,808 shares of AMTM common stock at a stated price of $0.00 per share upon vesting.

In connection with this vesting, 750 shares of AMTM common stock were tendered at $30.70 per share for tax withholding, a non-open-market, tax-related disposition. After these transactions, Arnette directly held 96,357 shares of AMTM common stock.

Insider Trade Summary

2,808 shares exercised/converted

Mixed 3 txns

Insider Arnette Stephen A

Role Chief Operating Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	2,808	$0.00	--
Exercise	Common Stock	2,808	$0.00	--
Tax Withholding	Common Stock	750	$30.70	$23K

Holdings After Transaction: Restricted Stock Units — 0 shares (Direct); Common Stock — 97,107 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 March 2, 2026.

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

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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^*

Arnette Stephen A

(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 Operating Officer

3. Date of Earliest Transaction (Month/Day/Year)
03/02/2026

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	03/02/2026		M		2,808	A	(1)	97,107	D
Common Stock	03/02/2026		F		750(2)	D	$30.7	96,357	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)	03/02/2026		M			2,808	(4)	(4)	Common Stock	2,808	$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 March 2, 2026.

Remarks:

	/s/ Michele T. St. Mary, Attorney-in-Fact	03/04/2026
	** 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.

FAQ

What insider transactions did Amentum (AMTM) COO Stephen Arnette report?

Stephen Arnette reported vesting of 2,808 restricted stock units into 2,808 AMTM common shares and a related tax-withholding share disposition. These transactions reflect routine equity compensation activity rather than open-market purchases or sales.

How many Amentum (AMTM) shares did the COO acquire through vesting?

The COO acquired 2,808 AMTM common shares through the vesting and conversion of 2,808 restricted stock units. Each restricted stock unit represented a contingent right to receive one share of AMTM common stock upon vesting on March 2, 2026.

How many Amentum (AMTM) shares were used for tax withholding in this Form 4?

A total of 750 AMTM common shares were tendered for tax withholding. This tax-related disposition occurred upon vesting of the restricted stock units and represents payment of tax liabilities using shares, not an open-market sale transaction.

What was the tax withholding share price in the Amentum (AMTM) Form 4?

The tax withholding disposition used a price of $30.70 per AMTM common share for 750 shares. This figure reflects the value applied to satisfy tax obligations related to the vesting of restricted stock units, as disclosed in the filing.

How many Amentum (AMTM) shares does the COO hold after these transactions?

Following the vesting and tax-withholding disposition, the COO directly holds 96,357 AMTM common shares. This post-transaction holding reflects the net position after receiving 2,808 vested shares and tendering 750 shares for tax withholding.

Were the Amentum (AMTM) insider transactions open-market buys or sells?

The transactions were not open-market buys or sells. They involved conversion of 2,808 restricted stock units into common shares and a tax-withholding disposition of 750 shares, which satisfied tax liabilities tied to the vesting event.