Amentum Holdings, Inc. Insider Trading Activity

Amentum Holdings, Inc. Chief Operating Officer Stephen A. Arnette reported routine equity compensation activity involving restricted stock units.

Rhea-AI Filing Summary

Amentum Holdings, Inc. Chief Operating Officer Stephen A. Arnette reported routine equity compensation activity involving restricted stock units. On May 6, 2026, 13,609 restricted stock units vested and were delivered as the same number of shares of AMTM common stock. Of these, 3,314 shares of common stock were tendered back to the company to satisfy tax withholding obligations, a non‑market disposition. As a result of these transactions, Arnette’s direct holdings increased, with the filing showing 109,966 shares of AMTM common stock held directly after the RSU-related activity.

Insider Trade Summary

13,609 shares exercised/converted

Exercise 3 txns

Insider Arnette Stephen A

Role Chief Operating Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	13,609	$0.00	$0.00
Exercise	Common Stock	13,609	$0.00	$0.00
Exercise Price or Tax Liability	Common Stock	3,314	$24.89	$82K

Holdings After Transaction: Restricted Stock Units — 13,609 contracts (Direct); Common Stock — 106,652 shares (Direct)

Footnotes (4)

1. F1. Represents distribution of AMTM common stock upon vesting of restricted stock units.
2. F2. Represents number of shares of AMTM common stock tendered for tax withholding upon vesting of restricted stock units.
3. F3. Each restricted stock unit represents a contingent right to receive one share of AMTM common stock.
4. F4. One-half of the restricted stock units shall vest and be delivered on the 18th month and three-year anniversaries of the date of grant.

Key Figures

RSUs vested: 13,609 units/shares Shares for tax withholding: 3,314 shares Direct holdings after transaction: 109,966 shares +1 more

4 metrics

RSUs vested 13,609 units/shares Restricted stock units vesting into AMTM common stock on May 6, 2026

Shares for tax withholding 3,314 shares Common shares tendered to cover tax obligations on RSU vesting

Direct holdings after transaction 109,966 shares AMTM common stock directly held by COO after Form 4 transactions

RSU-to-share ratio 1 RSU : 1 share Each restricted stock unit represents one share of AMTM common stock

Key Terms

Restricted Stock Units, tax withholding, derivative security, contingent right, +1 more

5 terms

Restricted Stock Units financial

"Represents distribution of AMTM common stock upon 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 financial

"Represents number of shares of AMTM common stock tendered for tax withholding upon vesting"

Tax withholding is the practice of taking a portion of a payment—such as wages, dividends, or sale proceeds—before it reaches the recipient and sending that portion to the tax authority as an advance on the recipient’s eventual tax bill. For investors it matters because withholding reduces immediate cash received and affects after‑tax returns, estimated tax payments, and whether you may owe more or receive a refund when taxes are finally calculated, like having a small automatic savings set aside for your tax bill.

derivative security financial

"transaction_code_description: Exercise or conversion of derivative security"

A derivative security is a financial contract whose value comes from the price or performance of something else, such as a stock, bond, commodity, or market index. For investors it acts like an insurance policy or a wager: it can be used to protect against losses, lock in prices, or amplify gains and losses, so it can change a portfolio’s risk and potential return without owning the underlying asset directly.

contingent right financial

"Each restricted stock unit represents a contingent right to receive one share"

vest and be delivered financial

"One-half of the restricted stock units shall vest and be delivered on the 18th month"

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

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Accepted by SEC EDGAR 05/07/2026 - 04:29 PM EDT 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^*

Arnette Stephen A

(Last) (First) (Middle)

C/O AMENTUM HOLDINGS, INC.

4800 WESTFIELDS BOULEVARD, SUITE 400

(Street)

CHANTILLY VIRGINIA 20151

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/06/2026

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	05/06/2026		M		13,609	A	(1)	109,966	D
Common Stock	05/06/2026		F		3,314(2)	D	$24.89	106,652	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)	05/06/2026		M			13,609	(4)	(4)	Common Stock	13,609	$0	13,609	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. One-half of the restricted stock units shall vest and be delivered on the 18th month and three-year anniversaries of the date of grant.

Remarks:

	/s/ Indira Lall, Attorney-in-Fact	05/07/2026
	** 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)