0000887343 colb:EBP001Member 2025-01-01 2025-12-31 0000887343 2025-01-01 2025-12-31 0000887343 0000887343 true true 11-K/A 11-K/A Columbia Banking System, Inc. Columbia Banking System, Inc. This Amendment No. 1 to the Annual Report on Form 11-K of the Columbia Banking System, Inc. Employee Stock Purchase Plan (the “Plan”) for the fiscal year ended December 31, 2025 is being filed solely to correct the auditor consent included as Exhibit 23.1 in the original filing. The consent has been replaced with the consent of the appropriate independent registered public accounting firm. No other changes have been made to the Form 11-K as originally filed with the U.S. Securities and Exchange Commission on March 31, 2026, and this Amendment does not modify or update any financial statements or other disclosures contained therein.