Stock Purchase Agreements; Standstill Agreements On December 8, 2022, Kite Pharma, Inc. ("Kite"), a subsidiary of Gilead, and Arcellx entered into a Collaboration and License Agreement (the "Collaboration Agreement") pursuant to which (1) Arcellx and Kite agreed to co-develop and co-commercialize CART-ddBCMA and next-generation autologous and non-autologous Chimeric Antigen Receptor T-cell (CAR-T) cell therapy products that use the same D-domain BCMA binder used in CART-ddBCMA, in each case for the treatment of multiple myeloma, and (2) Arcellx granted to Kite an option to include autologous CAR-T-cell therapy products that both utilize Arcellx's ARC-SparX platform and are directed to BCMA, such as ACLX-001, as well as ARC-SparX products directed to CS1. In connection with the Collaboration Agreement, on December 8, 2022, Gilead and Arcellx entered into the Stock Purchase Agreement, pursuant to which Gilead made the Initial Purchase, and a Standstill and Stock Restriction Agreement (the "Standstill Agreement"), pursuant to which Gilead agreed to certain transfer and standstill restrictions and received certain registration rights. On November 15, 2023, in connection with an amendment to the Collaboration Agreement, Gilead and Arcellx entered into the Second Stock Purchase Agreement, pursuant to which Gilead made the Additional Purchase, and amended and restated the Standstill Agreement (as amended, the "Amended and Restated Standstill Agreement"), pursuant to which Gilead agreed to certain additional standstill restrictions and received certain registration rights. On June 28, 2025, the standstill restrictions under the Amended and Restated Standstill Agreement expired. The foregoing descriptions of the Stock Purchase Agreement, the Second Stock Purchase Agreement and the Amended and Restated Standstill Agreement are not complete and are subject to and qualified in their entirety by reference to the full text of such agreements, which are attached as Exhibits 99.1, 99.2 and 99.3, hereto and incorporated herein by reference. Merger Agreement On February 13, 2026, Gilead submitted to the chief executive officer of Arcellx a non-binding proposal to acquire all of the outstanding shares of Common Stock that are not owned by Gilead or its subsidiaries for a purchase price of $98.00 per share in cash (the "Proposal"). The Proposal was approved by Gilead's board of directors earlier on the same day. The Proposal and board approval followed assessment of alternatives for the collaboration and relationship between Gilead and Arcellx, including maintaining the status quo. From February 13, 2026 through February 22, 2026, representatives of Gilead and Arcellx negotiated the terms of the transaction reflected in the Merger Agreement (defined below). On February 18, 2026, Gilead and Arcellx executed a non-disclosure agreement containing a standstill provision, and the standstill provision terminated upon the execution of the Merger Agreement. On February 22, 2026, Gilead, Arcellx and Purchaser entered into an Agreement and Plan of Merger (the "Merger Agreement"). Pursuant to the Merger Agreement, and upon the terms and subject to the conditions therein, Purchaser will commence a tender offer (the "Offer") to acquire all of the issued and outstanding shares of Common Stock in exchange for (x) $115.00 per share (the "Closing Amount"), net to the seller in cash, without interest, subject to any applicable withholding tax, and (y) one contractual contingent value right (a "CVR"), which represents the right to receive one contingent payment of $5.00 per CVR, in cash, without interest, upon the achievement of a specified milestone in accordance with the terms and subject to the conditions of a contingent value rights agreement, to be entered into with a rights agent selected by Parent and reasonably acceptable to the Company. The Offer will remain open for a minimum of 20 business days, subject to possible extension pursuant to the terms of the Merger Agreement. The obligation of Purchaser to consummate the Offer is subject to the satisfaction or waiver of customary conditions, including, among others, (i) there being validly tendered, and not validly withdrawn, in the Offer a number of Shares that, considered together with all other Shares owned by Purchaser and its affiliates, represent one more Share than 50% of the total number of Shares outstanding at the expiration of the Offer, (ii) the expiration or termination of the waiting period applicable to the Offer under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, and other specified notices, approvals or clearances in accordance with foreign antitrust laws having been given and obtained, (iii) the absence of any law or order prohibiting the consummation of the Offer or the Merger in any jurisdiction in which Parent or the Company has material business operations and (iv) other customary conditions set forth in Annex I to the Merger Agreement. Following the consummation of the Offer and subject to the terms and conditions of the Merger Agreement, Purchaser will merge with and into the Company pursuant to Section 251(h) of the General Corporation Law of the State of Delaware (the "DGCL"), with the Company being the surviving corporation (the "Merger"). At the effective time of the Merger, each Share (other than (i) Shares owned by the Company (including shares held in the Company's treasury), (ii) Shares owned both as of the date of the commencement of the Offer and immediately prior to the effective time of the Merger by Parent, Purchaser, or any other direct or indirect wholly owned subsidiary of Parent, (iii) Shares irrevocably accepted for purchase pursuant to the Offer and (iv) Shares held by stockholders who have properly exercised and perfected their demands for appraisal of such Shares in accordance with the DGCL and have neither withdrawn nor lost such rights prior to the effective time of the Merger) will be converted into the right to receive (A) the Closing Amount in cash, in each case without any interest thereon, subject to any withholding of taxes, plus (B) one (1) CVR. Tender and Support Agreements In connection with execution of the Merger Agreement, Gilead and Purchaser entered into Tender and Support Agreements (each, a "Tender and Support Agreement"), dated as of February 22, 2026 with each of (i) entities affiliated with SR One Capital, (ii) entities affiliated with New Enterprise Associates and (iii) each director and officer and certain other members of management of Arcellx (each, a "Supporting Stockholder" and, collectively, the "Supporting Stockholders"), which collectively own 6,033,683 Shares (collectively the "Supporting Stockholder Shares") (not including an additional 5,966,526 stock options and 3,016,601 restricted stock units that are subject to the Tender and Support Agreements), which represented approximately 10.3% of the outstanding Shares as of February 19, 2026, based on information provided by the Supporting Stockholders and Arcellx. Each Tender and Support Agreement provides that the Supporting Stockholder will, among other things, (i) tender all of its or his or her Supporting Stockholder Shares, (ii) vote against other proposals to acquire Arcellx and for any proposal for the Merger and (iii) agree to certain other restrictions on its or his respective ability to take actions with respect to Arcellx and its or his or her Supporting Stockholder Shares. The form of Tender and Support Agreement has been included to provide information regarding its terms. It is not intended to modify or supplement any factual disclosures about the applicable Supporting Stockholder or Arcellx, Gilead or Purchaser in any public reports filed with the Securities and Exchange Commission (the "SEC") by Arcellx, Gilead or Purchaser. The foregoing descriptions of the Merger Agreement and the Tender and Support Agreements, and the respective transactions contemplated thereby, do not purport to be complete and are qualified in their entirety by reference to such agreements. A copy of the Merger Agreement, listed as Exhibit 99.4 hereto, is incorporated by reference to Exhibit 2.1 to Gilead's Current Report on Form 8-K filed with the SEC on February 23, 2026. A copy of the form of Tender and Support Agreement, listed as Exhibit 99.5 hereto, is incorporated by reference to Exhibit 10.1 to Gilead's Current Report on Form 8-K filed with the SEC on February 23, 2026. Additional Information The purpose of the Offer is for Gilead, through Purchaser, to acquire control of Arcellx. The Offer would be the first step in Gilead's acquisition of Arcellx. The Offer is intended to facilitate the acquisition of all issued and outstanding Shares. The purpose of the Merger is to acquire all issued and outstanding Shares not tendered and purchased pursuant to the Offer. If the Offer is consummated, Purchaser intends to complete the Merger as soon as practicable thereafter. Following the Merger, Arcellx will become a wholly owned subsidiary of Gilead. In addition, Gilead will cause the Shares to be delisted from the Nasdaq Global Select Market and deregistered under the Act. The tender offer described in this document has not yet commenced. This communication is for informational purposes only and is neither an offer to purchase nor a solicitation of an offer to sell securities of Arcellx, nor is it a substitute for any tender offer materials that Gilead, Purchaser or Arcellx will file with the SEC. A solicitation and an offer to buy securities of Arcellx will be made only pursuant to an offer to purchase and related materials that Gilead intends to file with the SEC. At the time the tender offer is commenced, Gilead will file a Tender Offer Statement on Schedule TO with the SEC, and Arcellx will file a Solicitation/Recommendation Statement on Schedule 14D-9 with the SEC with respect to the tender offer. ARCELLX'S STOCKHOLDERS AND OTHER INVESTORS ARE URGED TO READ THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER TENDER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9 BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE WITH RESPECT TO THE TENDER OFFER. The Offer to Purchase, the related letter of transmittal and certain other tender offer documents, as well as the Solicitation/Recommendation Statement on Schedule 14D-9, will be sent to all stockholders of Arcellx at no expense to them. The Tender Offer Statement on Schedule TO, the Solicitation/Recommendation Statement on Schedule 14D-9 and other related documents will be made available for free at the SEC's web site at www.sec.gov. Additional copies may be obtained for free by contacting Gilead or Arcellx. Free copies of these materials and certain other offering documents will be made available by Gilead by mail to Gilead Sciences, Inc., 333 Lakeside Drive, Foster City, CA 94404, attention: Investor Relations, by phone at 1-800-GILEAD-5 or 1-650-574-3000, or by directing requests for such materials to the information agent for the offer, which will be named in the Tender Offer Statement on Schedule TO. Investors and security holders of Arcellx may also obtain, free of charge, the Solicitation/Recommendation Statement on Schedule 14D-9 and other related documents that Arcellx has filed with or furnished to the SEC under "SEC Filings" in the "Financials" section of Arcellx's website at https://ir.arcellx.com/financials/sec-filings/default.aspx. In addition to the Offer to Purchase, the related Letter of Transmittal and certain other tender offer documents, as well as the Solicitation/Recommendation Statement, Gilead and Arcellx file annual, quarterly and current reports, proxy statements and other information with the SEC. Gilead's and Arcellx's filings with the SEC are also available for free to the public from commercial document-retrieval services and at the website maintained by the SEC at www.sec.gov.