Amentum (NYSE: AMTM) CGO reports RSU vesting and tax-withholding share tender

Filing Impact

(Neutral)

Filing Sentiment

(Neutral)

Form Type

Rhea-AI Filing Summary

Amentum Holdings, Inc. Chief Growth Officer Sean Thomas Mullen reported routine equity compensation activity involving restricted stock units and related tax withholding. On May 6, 2026, 9,072 restricted stock units were exercised into an equal number of AMTM common shares, reflecting vesting of stock-based awards.

In connection with this vesting, 2,762 shares of AMTM common stock were tendered to cover tax withholding obligations, a non-market disposition. Following these transactions, Mullen directly held 35,210 shares of AMTM common stock and 9,073 restricted stock units, which vest in two installments on the 18-month and three-year anniversaries of the grant date.

Insider Trade Summary

9,072 shares exercised/converted

Mixed 3 txns

Insider Mullen Sean Thomas

Role Chief Growth Officer

Type	Security	Shares	Price	Value
Exercise	Restricted Stock Units	9,072	$0.00	--
Exercise	Common Stock	9,072	$0.00	--
Tax Withholding	Common Stock	2,762	$24.89	$69K

Holdings After Transaction: Restricted Stock Units — 9,073 shares (Direct, null); Common Stock — 35,210 shares (Direct, null)

Footnotes (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. Each restricted stock unit represents a contingent right to receive one share of AMTM common stock. 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 exercised: 9,072 units Shares for tax withholding: 2,762 shares Common shares after transactions: 35,210 shares +3 more

6 metrics

RSUs exercised 9,072 units Restricted stock units converted into AMTM common stock on May 6, 2026

Shares for tax withholding 2,762 shares AMTM common stock tendered to cover tax obligations on May 6, 2026

Common shares after transactions 35,210 shares Direct AMTM common stock holdings following reported Form 4 transactions

RSUs remaining 9,073 units Restricted stock units held after vesting and delivery activity

RSU vesting schedule Two installments One-half vests at 18 months and one-half at three years from grant

Tax-withholding price reference $24.89 per share Value used for the 2,762 shares tendered for tax withholding

Key Terms

Restricted Stock Units, tax withholding, derivative exercise/conversion, 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 of restricted stock."

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 exercise/conversion financial

"transaction_action: derivative exercise/conversion"

contingent right financial

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

vesting financial

"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."

Vesting is the process by which you earn full ownership of something, like company stock or a retirement benefit, over time. It’s like earning the right to keep a gift piece by piece the longer you stay with a company, making sure employees stay committed before they receive all the benefits.

Form 4 Insider Transactions: What Each Field Means →

05/07/2026 - 04:31 PM

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

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 Growth 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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	05/06/2026		M		9,072	A	⁽¹⁾	35,210	D
Common Stock	05/06/2026		F		2,762⁽²⁾	D	$24.89	32,448	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)
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)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Restricted Stock Units	⁽³⁾	05/06/2026		M			9,072	⁽⁴⁾	⁽⁴⁾	Common Stock	9,072	$0	9,073	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.

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)

Source: View Original Filing on SEC EDGAR

FAQ

What transactions did Amentum (AMTM) Chief Growth Officer report on this Form 4?

Sean Thomas Mullen reported vesting and exercise of 9,072 restricted stock units into AMTM common shares and a related tax-withholding share disposition of 2,762 shares, all as part of routine equity compensation rather than open-market buying or selling.

Did Amentum (AMTM) Chief Growth Officer sell shares in the open market?

No open-market sale was reported. Instead, 2,762 AMTM shares were tendered to satisfy tax withholding obligations tied to restricted stock vesting, which is classified as a tax-withholding disposition rather than a discretionary sale into the market.

How many Amentum (AMTM) shares does the Chief Growth Officer hold after these transactions?

After the reported vesting and tax withholding transactions, Sean Thomas Mullen directly holds 35,210 shares of AMTM common stock, according to the Form 4, reflecting his updated equity position following the distribution of vested restricted stock units.

What happened to the restricted stock units (RSUs) reported by Amentum (AMTM) Chief Growth Officer?

9,072 restricted stock units converted into an equal number of AMTM common shares upon vesting. Each RSU represents a contingent right to receive one AMTM share, and vesting triggers this distribution as part of the company’s stock-based compensation program.

How many restricted stock units does the Amentum (AMTM) Chief Growth Officer still hold?

Following the vesting transaction, the Form 4 shows that Sean Thomas Mullen holds 9,073 restricted stock units. These RSUs are scheduled so that one-half vests and is delivered at the 18‑month anniversary and the three‑year anniversary of the original grant date.

Are the Amentum (AMTM) RSU vesting terms time-based for the Chief Growth Officer?

Yes. The filing states that one-half of the restricted stock units will vest and be delivered on the 18‑month anniversary of the grant date, with the remaining half vesting and being delivered on the three‑year anniversary, reflecting time-based vesting conditions.