Arcellx (ACLX) CFO reports tax-driven share sale after exercising 20,530 units

Rhea-AI Filing Summary

Arcellx, Inc.’s chief financial officer, Michelle Gilson, reported two stock transactions involving the company’s common stock. On February 25, 2026, she sold 11,219 shares in an open-market, broker-assisted sale at a weighted average price of $113.8207 per share, primarily to cover tax withholding on previously vested restricted stock units. Earlier, on January 6, 2026, she acquired 20,530 shares at $0.00 per share through the exercise or conversion of a derivative security. After these transactions, she held 33,938 shares directly.

Insights

Insider trading and governance analyst

CFO reports tax-related sale and option exercise with modest net share reduction.

The chief financial officer of Arcellx, Inc. recorded an exercise of 20,530 derivative-linked shares at $0.00 on January 6, 2026, followed by an 11,219-share open-market sale at a weighted average of $113.8207 on February 25, 2026.

A footnote states the sale was broker-assisted to satisfy tax withholding from restricted stock unit vesting, indicating it was driven by tax obligations rather than a purely discretionary liquidation. Following these moves, her direct holdings stand at 33,938 shares.

From a governance perspective, such tax-withholding sales and derivative exercises are common elements of equity compensation programs. The filing does not quantify her holdings relative to total shares outstanding, so the broader ownership impact must be assessed using additional company disclosures.

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^*

Gilson Michelle

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CHIEF FINANCIAL OFFICER

3. Date of Earliest Transaction (Month/Day/Year)
02/25/2026

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(1)	01/06/2026		M		20,530	A	$0	64,832	D
Common Stock	02/25/2026		S(2)		11,219	D	$113.8207(3)	33,938	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. Each restricted stock unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock. Vesting of these RSUs previously reported in the Form 4 filed January 6, 2026.

2. Represents a broker-assisted sale to satisfy the Reporting Person's tax withholding obligations in connection with the vesting of restricted stock units.

3. Represents the weighted average share price of an aggregate total of 11,219 shares sold in the price range of $113.765 to $113.835 by the Reporting Person. The Reporting Person undertakes to provide upon request by the Commission staff, the issuer or a security holder of the issuer, full information regarding the number of shares sold at each separate price.

	/s/ Michelle Gilson	02/25/2026
	** 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).
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FAQ

What insider transactions did Arcellx (ACLX) report for CFO Michelle Gilson?

Arcellx’s CFO reported exercising 20,530 derivative-linked shares at $0.00 on January 6, 2026 and selling 11,219 shares on February 25, 2026. The sale was open-market and broker-assisted, primarily to cover tax withholding from vested restricted stock units.

How many Arcellx (ACLX) shares did the CFO sell and at what price?

The CFO sold 11,219 shares of Arcellx common stock in an open-market, broker-assisted transaction. The weighted average sale price was $113.8207 per share, across a price range from $113.765 to $113.835, as detailed in the filing footnotes.

Why did the Arcellx (ACLX) CFO sell 11,219 shares of common stock?

The 11,219-share sale was conducted to satisfy tax withholding obligations related to the vesting of restricted stock units. A footnote explains it was a broker-assisted transaction, indicating the sale was tied to compensation-related taxes rather than a purely discretionary liquidation.

What was the Arcellx (ACLX) CFO’s shareholding after these Form 4 transactions?

After the reported transactions, the Arcellx CFO directly owned 33,938 shares of common stock. This figure reflects both the 20,530-share derivative exercise on January 6, 2026 and the subsequent 11,219-share open-market sale on February 25, 2026 disclosed in the filing.

What derivative-related transaction did the Arcellx (ACLX) CFO report on January 6, 2026?

On January 6, 2026, the CFO reported a derivative exercise or conversion involving 20,530 shares of common stock at $0.00 per share. This transaction reflects equity compensation mechanics, increasing her direct holdings before the later tax-related share sale.