Sec Form 3 Filing - Grant-Huerta Yanina @ Atara Biotherapeutics, Inc. - 2025-03-31

FORM 3 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 Grant-Huerta Yanina 2. Issuer Name and Ticker or Trading Symbol Atara Biotherapeutics, Inc. [ ATRA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Accounting Officer (Last) (First) (Middle) C/O ATARA BIOTHERAPEUTICS, INC., 1280 RANCHO CONEJO BOULEVARD 3. Date of Earliest Transaction (MM/DD/YY) 03/31/2025 (Street) THOUSAND OAKS, CA91320 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 39,285 ( 1 ) ( 2 ) 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 Employee Stock Option (Right to Buy) $ 198 04/06/2024 04/30/2030 Common Stock 800 D Employee Stock Option (Right to Buy) $ 97.75 03/01/2025 02/28/2033 Common Stock 1,100 D Employee Stock Option (Right to Buy) $ 97.75 ( 3 ) 02/28/2033 Common Stock 550 D Employee Stock Option (Right to Buy) $ 11 07/31/2024 01/05/2034 Common Stock 275 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Grant-Huerta Yanina C/O ATARA BIOTHERAPEUTICS, INC. 1280 RANCHO CONEJO BOULEVARD THOUSAND OAKS, CA91320 Chief Accounting Officer Signatures /s/ John Chao, Attorney-in-Fact for Yanina Grant-Huerta 04/10/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes an aggregate 33,840 restricted stock units ("RSUs"), which are comprised of: (i) 51 RSUs that vest on November 15, 2025; (ii) 3,614 RSUs that vest as to 1/4th of the shares on May 15, 2025, and each of the next three (3) Quarterly Vesting Dates (as defined herein); (iii) 1,125 RSUs that vest as to 1/5th of the shares on May 15, 2025, and each of the next four (4) Quarterly Vesting Dates; and (iv) 29,050 RSUs that vest as to 1/8th of the shares on May 15, 2025, and each of the next seven (7) Quarterly Vesting Dates, each of which is subject to the reporting person's continuous service. ( 2 )"Quarterly Vesting Date" means March 1, May 15, August 15, and November 15 of each year, provided that if such date falls on a weekend or holiday, the "Quarterly Vesting Date" shall be the first (1st) business day after such date. ( 3 )1/12th of the shares subject to the stock option vested and became exercisable on April 1, 2025, and the remaining shares vest in equal monthly installments over the following eleven (11) months, subject to the reporting person's continuous service.

Remarks: Exhibit List: Exhibit 24 - Power of Attorney

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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