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 Date of Report (Date of earliest event reported): February 28, 2024 Arcellx, Inc. (Exact name of Registrant as Specified in Its Charter) Delaware 001-41259 47-2855917 (State or Other Jurisdiction (Commission File Number) (IRS Employer of Incorporation) Identification No .) 800 Bridge Parkway Suite A Redwood City, California 94065 (Address of P ...