UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Fiscal Year EndedDecember 31, 2023 Commission File No.001-16209 ARCH CAPITAL GROUP LTD. (Exact name of registrant as specified in its charter) Bermuda 98-0374481 (State or other jurisdiction of incorporation or organization) (I.R.S. Employer ...