X0609 4 2026-06-09 0001604464 Atara Biotherapeutics, Inc. ATRA 0002023732 Ciongoli Gregory Austin false C/O ATARA BIOTHERAPEUTICS, INC. 1280 RANCHO CONEJO BOULEVARD THOUSAND OAKS CA 91320 true false true true See Remarks false Common Stock 2026-06-09 4 A false 12000 0 A 12000 D Common Stock 1209395 I See Footnote These restricted stock units shall vest on the earlier of June 9, 2027 or the date of the next annual meeting of stockholders, subject to the Reporting Person's continuous service. The securities reported on this row are directly held by Adiumentum Capital Fund I LP, a limited partnership organized under the laws of Delaware ("Adiumentum"). Adiumentum Capital Fund I GP LLC, a limited liability company organized under the laws of Delaware ("Adiumentum GP"), is the general partner of Adiumentum. Gregory A. Ciongoli is the managing partner of Adiumentum and the managing member of Adiumentum GP. Each of Adiumentum, Adiumentum GP, and Mr. Ciongoli may be deemed to have the shared power to vote or direct the vote (and the shared power to dispose or direct the disposition of) the securities that are directly held by Adiumentum. Each of Adiumentum, Adiumentum GP, and Mr. Ciongoli may be deemed to have a pecuniary interest in the securities that are directly held by Adiumentum, but disclaims any beneficial ownership of such securities, except to the extent of any pecuniary interest therein. Exhibit List: Exhibit 24 - Power of Attorney. Mr. Ciongoli serves as a director on the Board of Directors of the Issuer and, as a result, Adiumentum and Adiumentum GP are directors by deputization for purposes of Section 16 of the Securities Exchange Act of 1934, as amended. Neither Adiumentum nor Adiumentum GP have a pecuniary interest in the restricted stock units awarded to Mr. Ciongoli as reported in this Form 4, and therefore Adiumentum and Adiumentum GP have been excluded as reporting persons from this Form 4. /s/ John Chao, Attorney-in-Fact for Gregory A. Ciongoli 2026-06-11