ACLX Form 4: CEO forfeits 546,938 shares for tax withholding; owns 617,919

Rhea-AI Filing Summary

Arcellx insider transaction: Rami Elghandour, President, CEO and Chairman, reported a disposition of 546,938 shares of Arcellx common stock on 08/28/2025 at a reported price of $70.25 per share. The filing states these shares were forfeited to satisfy the reporting person’s tax withholding obligations in connection with the settlement of performance-based restricted stock units that vested on February 27, 2025. After the reported disposition, the reporting person beneficially owns 617,919 shares. The Form 4 was signed by an attorney-in-fact on 08/29/2025.

Positive

• Reporting includes explanatory remark that the disposition was to satisfy tax withholding on vested performance-based RSUs, clarifying the nature of the transaction
• Reporting person retains material ownership after the transaction: 617,919 shares remain beneficially owned

Negative

• Large number of shares disposed: 546,938 shares were forfeited on 08/28/2025 at a reported price of $70.25 per share

Insights

Financial Analyst

TL;DR: CEO reported a large share disposition tied to tax withholding on vested performance awards; ownership remains material.

The transaction is explicitly described as forfeiture to satisfy tax withholding for vested performance-based RSUs, indicating this was a compensatory, not market-sale, event. The reported price of $70.25 and the quantity disposed (546,938 shares) materially reduced the reporting person’s holdings but left a sizeable stake of 617,919 shares, maintaining alignment with shareholders. Impact on share supply is limited to the forfeited amount and arises from internal compensation mechanics rather than new outside selling pressure.

Corporate Governance Expert

TL;DR: Insider disposition was for tax withholding on vested awards; governance disclosure is timely and includes an explanation.

The Form 4 discloses the relationship (President, CEO, Chairman) and provides a clear explanatory remark that the shares were forfeited to satisfy tax withholding from performance-based RSUs vested earlier. The timely filing and the explanatory note meet standard disclosure expectations for Section 16 reporting. There is no indication of other transactions or plans in this filing.

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^*

Elghandour Rami

(Last) (First) (Middle)

C/O ARCELLX, INC

800 BRIDGE PARKWAY

(Street)

REDWOOD CITY CA 94065

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Arcellx, Inc. [ ACLX ]

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

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	SEE REMARKS

3. Date of Earliest Transaction (Month/Day/Year)
08/28/2025

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	08/28/2025		F		546,938(1)	D	$70.25	617,919	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. Shares forfeited to satisfy the Reporting Person's tax withholding obligations in connection with the settlement of performance-based restricted stock units which vested on February 27, 2025, as previously reported in the Form 4 filed February 27, 2025.

Remarks:

President, CEO and Chairman of the Board

	/s/ Michelle Gilson, as Attorney-in-Fact	08/29/2025
	** 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.
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FAQ

What did Arcellx CEO Rami Elghandour report on Form 4 (ACLX)?

The Form 4 reports a disposition of 546,938 shares on 08/28/2025 at a reported price of $70.25 per share.

Why were the 546,938 Arcellx shares disposed?

The filing states the shares were forfeited to satisfy tax withholding obligations related to performance-based restricted stock units that vested on February 27, 2025.

How many Arcellx shares does the reporting person own after the transaction?

After the reported disposition, the reporting person beneficially owns 617,919 shares.

What is the reporting person’s role at Arcellx?

The reporting person is identified as President, CEO and Chairman of the Board.

When was the Form 4 signed and by whom?

The Form 4 bears a signature by an attorney-in-fact, /s/ Michelle Gilson, dated 08/29/2025.