X0202 SCHEDULE 13D/A 0001104659-25-052422 0001425738 XXXXXXXX LIVE 3 Common Stock, par value $0.0001 per share 07/22/2026 true 0001604464 046513206 Atara Biotherapeutics, Inc.

1280 Rancho Conejo Blvd Thousand Oaks CA 91320

Redmile Group, LLC (415) 489-9980 900 Larkspur Landing Circle, Suite 270 Larkspur CA 94939 0001425738 N Redmile Group, LLC OO N DE 0.00 950994.00 0.00 950994.00 950994.00 N 9.9 IA OO (1) The source of funds was working capital of certain private investment funds managed by Redmile Group, LLC (the "Redmile Funds"), including Redmile Biopharma Investments II, L.P. ("RBI II") and Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only"). (2) The information in Item 5(a) relating to the shares of common stock, par value $0.0001 per share, of the Issuer (the "Common Stock") that are or may be deemed beneficially owned by Redmile Group, LLC ("Redmile") and the calculation of the percent of such class of securities is incorporated by reference herein. 0001650527 N Green Jeremy OO N X0 0.00 950994.00 0.00 950994.00 950994.00 N 9.9 IN HC (1) The source of funds was working capital of the Redmile Funds, including RBI II and Redmile Long Only. (2) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Jeremy Green and the calculation of the percent of such class of securities is incorporated by reference herein. 0001772230 N Redmile Biopharma Investments II, L.P. WC N DE 0.00 631020.00 0.00 631020.00 631020.00 N 6.6 PN (1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by RBI II and the calculation of the percent of such class of securities is incorporated by reference herein. 0002048243 N Redmile Strategic Long Only Trading Sub, Ltd. WC N E9 0.00 401901.00 0.00 401901.00 401901.00 N 4.2 CO (1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Redmile Long Only and the calculation of the percent of such class of securities is incorporated by reference herein. Common Stock, par value $0.0001 per share Atara Biotherapeutics, Inc. 1280 Rancho Conejo Blvd Thousand Oaks CA 91320 This Amendment No. 3 to Schedule 13D (this "Amendment") amends and supplements the Schedule 13D filed with the SEC on May 23, 2025, which was previously amended and supplemented by that Amendment No. 1 to Schedule 13D filed with the SEC on November 14, 2025 and that Amendment No. 2 to Schedule 13D filed with the SEC on May 14, 2026 (collectively, the "Prior Schedule 13D"). This Amendment reports the exercise of certain pre-funded warrants to purchase Common Stock (the "Warrants") by Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only") and Redmile Biopharma investments II, L.P. ("RBI II" and collectively with Redmile Long Only, Redmile Group, LLC and Jeremy Green, the "Reporting Persons") described in Item 5(a) below and the resulting change in the beneficial ownership of Redmile Long Only following such exercise. Capitalized terms used but not defined in this Amendment shall have the meanings set forth in the Prior Schedule 13D. Except as specifically amended by this Amendment, the Prior Schedule 13D is unchanged. On July 16, 2026, Redmile Group, LLC ("Redmile") exercised certain Warrants held by RBI II and Redmile Long Only through a "cashless exercise" to acquire the Issuer's Common Stock. The transactions resulted in the Issuer (i) withholding 53 shares of Common Stock from RBI II and 7 shares of Common Stock from Redmile Long Only to pay the exercise price under the terms of the Warrants and (ii) issuing the remaining 174,247 shares of Common Stock to RBI II and 20,904 shares of Common Stock to Redmile Long Only. Item 5(a) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: The aggregate amount of shares of Common Stock that may be deemed beneficially owned by the Reporting Persons is comprised of (i) 636,852 shares of Common Stock held by certain investment vehicles for which Redmile is the investment manager (the "Redmile Funds"), including the 316,878 shares of Common Stock directly held by RBI II and the 87,759 shares of Common Stock directly held by Redmile Long Only, and (ii) 314,142 shares of Common Stock issuable to the Redmile Funds, including RBI II and Redmile Long Only, upon exercise of certain Warrants, which is the maximum number of shares of Common Stock that could be issued upon exercise of the Warrants under the 9.99% beneficial ownership limitation (the "Beneficial Ownership Limitation"). The Redmile Funds hold Warrants that may be exercised into 3,217,632 shares of Common Stock issuable upon exercise of the Warrants, including the 1,879,855 shares of Common Stock issuable upon exercise of the remaining Warrants directly held by RBI II, and the 806,670 shares of Common Stock issuable upon exercise of the remaining Warrants directly held by Redmile Long Only, each of which is subject to the Beneficial Ownership Limitation. All of the reported securities are directly owned by certain Redmile Funds, including RBI II and Redmile Long Only. Redmile may be deemed to beneficially own these securities in its capacity as their investment manager with discretion to vote and dispose of the securities held by the Redmile Funds. Mr. Green also may be deemed to beneficially own these securities as the principal of Redmile. Redmile and Mr. Green each disclaim beneficial ownership of these securities, except to the extent of its or his pecuniary interest in such securities, if any. Percentage based on the sum of: (i) 9,010,172 shares of Common Stock outstanding as of May 8, 2026, as reported by the Issuer in its Form 10-Q for the quarterly period ended March 31, 2026 filed with the Securities and Exchange Commission on May 12, 2026, plus (ii) 195,151 shares of Common Stock issued to RBI II and Redmile Long Only upon exercise of certain Warrants, plus (iii) 314,142 shares of Common Stock issuable upon exercise of certain Warrants directly held by the Redmile Funds, which due to the Beneficial Ownership Limitation is the maximum number of shares that could be issued upon exercise of those Warrants. Item 5(b) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: Redmile: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 Jeremy C. Green: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 RBI II: (1) Sole Voting Power: 0 (2) Shared Voting Power: 631,020 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 631,020 Redmile Long Only: (1) Sole Voting Power: 0 (2) Shared Voting Power: 401,901 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 401,901 See the response to Item 3. Except as disclosed in Item 3, no reportable transactions were effected by any Reporting Persons during the past sixty days. Redmile Long Only ceased to be a 5% beneficial owner on July 22, 2026 solely as a result of the exercise of the pre-funded warrants described in Item 3 above. Redmile Group, LLC /s/ Jeremy C. Green 07/24/2026 Green Jeremy /s/ Jeremy C. Green 07/24/2026 Redmile Biopharma Investments II, L.P. /s/ Jeremy C. Green 07/24/2026 Redmile Strategic Long Only Trading Sub, Ltd. /s/ Jeremy C. Green 07/24/2026