David Charles Lubner - 20 Jan 2026 Form 4 Insider Report for Arcellx, Inc. (ACLX)

Role: Director
Signature: /s/ Michelle Gilson, as Attorney-in-Fact
Issuer symbol: ACLX
Transactions as of: 20 Jan 2026
Net transactions value: -$412,320
Form type: 4
Filing time: 20 Jan 2026, 19:59:40 UTC
Previous filing: 19 Aug 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Lubner David Charles	Director	C/O ARCELLX, INC., 800 BRIDGE PARKWAY, REDWOOD CITY	/s/ Michelle Gilson, as Attorney-in-Fact	20 Jan 2026	0001572000

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	ACLX	Common Stock	Options Exercise	$37,680	+6,000	+28%	$6.28	27,659	20 Jan 2026	Direct
transaction	ACLX	Common Stock	Sale	$450,000	-6,000	-22%	$75.00	21,659	20 Jan 2026	Direct	F1

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	ACLX	Stock Option (right to buy)	Options Exercise	$0	-6,000	-9.2%	$0.000000	59,405	20 Jan 2026	Common Stock	6,000	$6.28	Direct	F2

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Buy Plan / Sale Plan: These are also open market purchases/sales of shares, but in this case the transaction is part of a trading plan. Rule 10b5-1 allows insiders to setup a trading plan to buy/sell stocks over a certain period of time. Since the purchases/sales are predetermined, this protects the insiders from violating insider trading law.

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).

Explanation of Responses:

Id	Content
F1	The sale of shares reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan entered into by the Reporting Person on September 29, 2025.
F2	Shares issued pursuant to the Issuer's 2017 Equity Incentive Plan (the "2017 Plan"). Subject to the Reporting Person continuing to be a Service Provider (as defined 2017 Plan) through each applicable date, one forty-eighth (1/48th) of the shares subject to the option shall vest each month following the Vesting Commencement Date on the same day of the month as the Vesting Commencement Date (and if there is no corresponding day, on the last day of the month). "Vesting Commencement Date" shall mean June 9, 2021.

Content

The sale of shares reported on this Form 4 was effected pursuant to a Rule 10b5-1 trading plan entered into by the Reporting Person on September 29, 2025.

Shares issued pursuant to the Issuer's 2017 Equity Incentive Plan (the "2017 Plan"). Subject to the Reporting Person continuing to be a Service Provider (as defined 2017 Plan) through each applicable date, one forty-eighth (1/48th) of the shares subject to the option shall vest each month following the Vesting Commencement Date on the same day of the month as the Vesting Commencement Date (and if there is no corresponding day, on the last day of the month). "Vesting Commencement Date" shall mean June 9, 2021.