Sec Form 4 Filing - Heery Christopher @ Arcellx, Inc. - 2024-03-22

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Heery Christopher 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 MEDICAL OFFICER (Last) (First) (Middle) C/O ARCELLX, INC., 800 BRIDGE PARKWAY 3. Date of Earliest Transaction (MM/DD/YY) 03/22/2024 (Street) REDWOOD CITY, CA94065 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 03/22/2024 M 20,000 A $ 6.28 50,303 D Common Stock 03/22/2024 S( 1 ) 10,057 D $ 69.5944 ( 2 ) 40,246 D Common Stock 03/22/2024 S( 1 ) 25,975 D $ 70.1327 ( 3 ) 14,271 D Common Stock 03/22/2024 S( 1 ) 4,333 D $ 71.3618 ( 4 ) 9,938 D Common Stock 03/22/2024 S( 1 ) 1,000 D $ 72.2474 ( 5 ) 8,938 D Common Stock 03/26/2024 M 5,450 A $ 6.28 14,388 D Common Stock 03/26/2024 S( 1 ) 2,555 D $ 68.5473 ( 6 ) 11,833 D Common Stock 03/26/2024 S( 1 ) 2,034 D $ 69.3604 ( 7 ) 9,799 D Common Stock 03/26/2024 S( 1 ) 861 D $ 70.1866 ( 8 ) 8,938 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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 Stock Option (right to buy) $ 6.28 03/22/2024 M 10,000 ( 9 ) 06/09/2031 Common Stock 10,000 $ 0 110,623 D Stock Option (right to buy) $ 6.28 03/22/2024 M 10,000 ( 10 ) 06/09/2031 Common Stock 10,000 $ 0 19,069 D Stock Option (right to buy) $ 6.28 03/26/2024 M 5,450 ( 9 ) 06/09/2031 Common Stock 5,450 $ 0 105,173 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Heery Christopher C/O ARCELLX, INC. 800 BRIDGE PARKWAY REDWOOD CITY, CA94065 CHIEF MEDICAL OFFICER Signatures /s/ Michelle Gilson, as Attorney-in-Fact 03/26/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )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 December 22, 2023. ( 2 )Represents the weighted average share price of an aggregate total of 10,057 shares sold in the price range of $68.87 to $69.8699 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. ( 3 )Represents the weighted average share price of an aggregate total of 25,975 shares sold in the price range of $69.87 to $70.8699 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. ( 4 )Represents the weighted average share price of an aggregate total of 4,333 shares sold in the price range of $70.87 to $71.8699 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. ( 5 )Represents the weighted average share price of an aggregate total of 1,000 shares sold in the price range of $71.92 to $72.9199 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. ( 6 )Represents the weighted average share price of an aggregate total of 2,555 shares sold in the price range of $67.90 to $68.8999 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. ( 7 )Represents the weighted average share price of an aggregate total of 2,034 shares sold in the price range of $68.92 to $69.9199 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. ( 8 )Represents the weighted average share price of an aggregate total of 861 shares sold in the price range of $69.92 to $70.9199 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. ( 9 )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, twenty-five percent (25%) of the shares subject to the option shall vest on the one (1) year anniversary of the Vesting Commencement Date, and one forty-eighth (1/48th) of the shares subject to the option shall vest each month thereafter 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 April 26, 2021. ( 10 )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.

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).

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