United States Securities and Exchange Commission Washington, D.C. 20549 FORM 10-Q ☒ Quarterly Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the quarterly period ended: March 31, 2023 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: 000-20288 COLUMBIA BANKING SYSTEM, INC. (Exact Name of Registrant as Specified in Its Charter) Washington 91-1422237 (State or Other Jurisd ...