UNITED STATES SECURITIES AND EXCHANGE COMMISSION FORM 10-K Washington, D.C. 20549 (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number 001-38419 Arcus Biosciences, Inc. (Exact name of Registrant as specified in its Charter) (State or other jurisdiction of incorporation or ...