COLUMBIA BANKING SYSTEM INC

On a quarterly basis, the Company carries out an evaluation, under the supervision and with the participation of our management, including our Chief Executive Officer, Principal Financial Officer, and Principal Accounting Officer, of the effectiveness of the design and operation of our disclosure controls and procedures pursuant to Rule 13a-15(b) under the Securities Exchange Act of 1934. As of December 31, 2024, our management, including our Chief Executive Officer, Principal Financial Officer, and Principal Accounting Officer, concluded that our disclosure controls and procedures were effective in timely alerting them to material information relating to us that is required to be included in our periodic SEC filings.

Although management changes and improves our internal controls over financial reporting on an ongoing basis, we do not believe that any such changes occurred in the fourth quarter 2024 that materially affected or are reasonably likely to materially affect our internal control over financial reporting.

REPORT OF MANAGEMENT ON INTERNAL CONTROL OVER FINANCIAL REPORTING

The management of Columbia Banking System, Inc. is responsible for establishing and maintaining adequate internal control over financial reporting as defined in Rule 13a-15(f) under the Securities Exchange Act of 1934. The Company's internal control system is designed to provide reasonable assurance to our management and Board regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. The Company's internal control over financial reporting includes those policies and procedures that:

•Pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the Company's assets;

•Provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the Company are being made only in accordance with the authorizations of management and directors of the Company; and

•Provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of the Company's assets that could have a material effect on the financial statements.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

Management assessed the effectiveness of the Company's internal control over financial reporting as of December 31, 2024. In making this assessment, management used the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission in Internal Control - Integrated Framework (2013). This assessment included controls over the preparation of the schedules equivalent to the basic financial statements in accordance with the instructions for the consolidated financial statements for Bank Holding Companies (Form FR Y-9C) to meet the reporting requirements of Section 112 of the Federal Deposit Insurance Corporation Improvement Act. Based on our assessment and those criteria, management believes that, as of December 31, 2024, the Company maintained effective internal control over financial reporting.

The Company's independent registered public accounting firm has audited the Company's consolidated financial statements that are included in this Annual Report on Form 10-K and the effectiveness of our internal control over financial reporting as of December 31, 2024 and issued their Report of Independent Registered Public Accounting Firm, appearing under Item 8 of this Annual Report on Form 10-K. The audit report expresses an unqualified opinion on the effectiveness of the Company's internal control over financial reporting as of December 31, 2024.

February 25, 2025