X0407 4 2023-05-11 1 0001786205 Arcellx, Inc. ACLX 0001853723 SR ONE CAPITAL MANAGEMENT, LLC 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0001848319 SR One Capital Fund I Aggregator LP 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0001853724 SR ONE CAPITAL PARTNERS I, LP 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0001595117 George Simeon 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0001867644 SR One Co-Invest II, LLC 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0001910324 SR One Co-Invest II Manager, LLC 985 OLD EAGLE SCHOOL ROAD SUITE 511 WAYNE PA 19087 0 0 1 0 0 Common Stock 2023-05-11 4 S 0 631932 45.00 D 2834879 I See Note 2 Common Stock 2023-05-11 4 S 0 370612 45.00 D 1662584 I See Note 3 Common Stock 2023-05-11 4 S 0 6485 46.15 D 2828394 I See Note 2 Common Stock 2023-05-11 4 S 0 3804 46.15 D 1658780 I See Note 3 The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $45.00 to $45.745 per share, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission (the "SEC"), upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The securities are directly held by SR One Capital Fund I Aggregator, LP ("SR One Fund I Aggregator"). SR One Capital Partners I, LP ("SR One Partners I") is the sole general partner of SR One Fund I Aggregator, and SR One Capital Management, LLC ("SR One Capital Management") is the sole general partner of SR One Partners I. Simeon George, M.D. is the managing member of SR One Capital Management (SR One Partners I, SR One Capital Management, and Dr. George together, the "Fund I Indirect Reporting Persons"). The Fund I Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended ("Section 16"), or otherwise of such portion of the securities held by SR One Fund I Aggregator in which the Fund I Indirect Reporting Persons have no pecuniary interest. The securities are directly held by SR One Co-Invest II, LLC ("SR One Co-Invest II"). SR One Co-Invest II Manager, LLC ("SR One Co-Invest II Manager") is the managing member of SR One Co-Invest II and SR One Capital Management is the managing member of SR One Co-Invest II Manager. Dr. George is the managing member of SR One Capital Management (SR One Co-Invest II Manager, SR One Capital Management, and Dr. George together, the "Co-Invest II Indirect Reporting Persons"). The Co-Invest II Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 or otherwise of such portion of the securities held by SR One Co-Invest II in which the Co-Invest II Indirect Reporting Persons have no pecuniary interest. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $46.00 to $46.56 per share, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. /s/ Sasha Keough, attorney-in-fact for SR One Capital Management, LLC 2023-05-15 /s/ Sasha Keough, attorney-in-fact for SR One Capital Fund I Aggregator, LP 2023-05-15 /s/ Sasha Keough, attorney-in-fact for SR One Capital Partners I, LP 2023-05-15 /s/ Sasha Keough, attorney-in-fact for Simeon George 2023-05-15 /s/ Sasha Keough, attorney-in-fact for SR One Co-Invest II, LLC 2023-05-15 /s/ Sasha Keough, attorney-in-fact for SR One Co-Invest II Manager, LLC 2023-05-15