X0202 SCHEDULE 13D/A 0000904454-26-000123 0000882095 XXXXXXXX LIVE 1 Common Stock, par value $0.001 04/28/2026 false 0001786205 03940C100 Arcellx, Inc.

800 BRIDGE PARKWAY REDWOOD CITY CA 94065

Gilead Sciences, Inc. 650-574-3000 333 Lakeside Drive, Foster City CA 94404 0000882095 N GILEAD SCIENCES, INC. WC N DE 100.00 0.00 100.00 0.00 100.00 N 100 CO * See Item 4. Common Stock, par value $0.001 Arcellx, Inc. 800 BRIDGE PARKWAY REDWOOD CITY CA 94065 Explanatory Note This Amendment No. 1 amends the Schedule 13D filed on February 23, 2026, by Gilead Sciences, Inc. ("Gilead") relating to shares of common stock, par value $0.001 per share ("Shares" or "Common Stock") of Arcellx, Inc. (the "Original Schedule 13D"). Except as set forth herein, the Original Schedule 13D is unmodified. Capitalized terms used by not otherwise defined in this Amendment No. 1 have the meanings set forth in the Original Schedule 13D. Item 4 of the Original Schedule 13D is amended to include the following at the end thereof: "As previously disclosed, Gilead, Purchaser and Arcellx entered into the Merger Agreement pursuant to which Purchaser commenced the Offer on March 6, 2026. The Offer expired at 5:00 p.m., Eastern Time, on April 27, 2026. Computershare Trust Company N.A., the depositary and paying agent for the Offer, advised Gilead that, as of the expiration of the Offer, 38,795,604 Shares had been validly tendered and not validly withdrawn pursuant to the Offer, representing, together with Shares already owned by Gilead, approximately 77.2% of the Shares outstanding as of the expiration of the Offer. Following consummation of the Offer, on April 28, 2026, Gilead completed its acquisition of Arcellx through the merger of Purchaser with and into Arcellx, and without a meeting of the stockholders of Arcellx in accordance with Section 251(h) of the DGCL, with Arcellx surviving such Merger as a wholly owned subsidiary of Gilead. In connection with the Merger, each Share issued and outstanding immediately prior to the effective time of the Merger (other than (i) Shares owned immediately prior to the effective time of the Merger by Arcellx (including those held in Arcellx's treasury), (ii) Shares owned both as of the commencement of the Offer and immediately prior to the effective time of the Merger by Gilead, Purchaser or any other direct or indirect wholly owned subsidiary of Gilead, (iii) Shares irrevocably accepted for purchase pursuant to the Offer and (iv) Shares held by stockholders who are entitled to appraisal rights under Section 262 of the DGCL and have properly exercised and perfected their respective demands for appraisal of such Shares in the time and manner provided in Section 262 of the DGCL and, as of the effective time of the Merger, have neither effectively withdrawn nor lost their rights to such appraisal and payment under the DGCL) was cancelled and converted into the right to receive on a per Share basis, (x) the Closing Amount in cash, without any interest thereon, subject to any withholding tax, plus (y) one CVR per Share (the Closing Amount plus one CVR, together, the "Offer Price"). As a result of the Merger, the 100 issued and outstanding shares of common stock, par value $0.001 per share, of Purchaser held by Gilead were converted into 100 issued and outstanding shares of common stock, par value $0.001 per share (the "New Shares"), of Arcellx. Consequently, Gilead became the beneficial owner of such 100 New Shares, which represent all of Arcellx's issued and outstanding shares of capital stock. Following the Merger, all Shares ceased trading prior to the opening of trading on the Nasdaq Global Select Market on April 28, 2026, and will be delisted from Nasdaq and deregistered under the Exchange Act." Item 5 of the Original Schedule 13D is hereby amended and restated in its entirety as follows: "(a)-(b) The information relating to the beneficial ownership of the Shares by Gilead set forth in Rows 7 through 13 on each of the cover pages hereto is incorporated by reference herein and is as of the date hereof. This Schedule 13D shall not be construed as an admission by Gilead that Gilead is, for the purposes of Section 13(d) of the Act, the beneficial owner of any Shares covered by this statement. "(a)-(b) The information relating to the beneficial ownership of the Shares by Gilead set forth in Rows 7 through 13 on each of the cover pages hereto is incorporated by reference herein and is as of the date hereof. This Schedule 13D shall not be construed as an admission by Gilead that Gilead is, for the purposes of Section 13(d) of the Act, the beneficial owner of any Shares covered by this statement. Except as otherwise described herein and in the Original Schedule 13D, neither Gilead nor, to the best knowledge of Gilead, any of the individuals listed on Schedule I have effected any transactions in Common Stock during the past sixty (60) days. On April 28, 2026, Purchaser accepted for payment pursuant to the Offer in exchange for the Offer Price all Shares validly tendered and not validly withdrawn pursuant to the Offer prior to the expiration of the Offer. Not applicable. Not applicable. Item 6 of the Original Schedule 13D is hereby amended and supplemented by adding the following at the end thereof: "At the effective time of the Merger, the Tender and Support Agreements terminated in accordance with their express terms." GILEAD SCIENCES, INC. /s/ Andrew D. Dickinson 04/28/2026