Date of Report (Date of earliest event reported): January 12, 2026 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Atara Biotherapeutics, Inc. (Exact name of Registrant as Specified in Its Charter) Delaware 001-36548 46-0920988 (State or Other Jurisdiction of Incorporation) (Commission File Number) (IRS Employer Identification No.) 1280 Rancho Conejo Blvd Thousand Oaks, California 91320 (Ad ...