Other Events. On Aug 14, 2026, Columbia Banking System, Inc., parent company of Columbia Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.37 per common share. The dividend is payable September 14, 2026, to shareholders of record as of August 28, 2026. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Director — Simone Lagomarsino: Ms. Lagomarsino was appointed to the Board of Directors and will serve on key committees.

Results of Operations and Financial Condition. On July 23, 2026, Columbia Banking System, Inc. issued a press release announcing second quarter 2026 financial results. The release is attached hereto as Exhibit 99.1. Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended June 30, 2026 as part of its quarterly report on Form 10-Q covering that period. The information contained in this paragraph, as well as Exhibit 99.1 referenced here…

Other Events. On May 15, 2026, Columbia Banking System, Inc., parent company of Columbia Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.37 per common share. The dividend is payable June 15, 2026, to shareholders of record as of May 29, 2026. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Results of Operations and Financial Condition. On April 23, 2026, Columbia Banking System, Inc. issued a press release announcing first quarter 2026 financial results. The release is attached hereto as Exhibit 99.1. Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended March 31, 2026 as part of its quarterly report on Form 10-Q covering that period. The information contained in this paragraph, as well as Exhibit 99.1 referenced her…

Other Events. On February 13, 2026, Columbia Banking System, Inc., parent company of Columbia Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.37 per common share. The dividend is payable March 16, 2026, to shareholders of record as of February 27, 2026. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Results of Operations and Financial Condition. On January 22, 2026, Columbia Banking System, Inc. issued a press release announcing fourth quarter and full year 2025 financial results. The release is attached hereto as Exhibit 99.1. Columbia Banking System, Inc. will include final financial statements and additional analyses for the year ended December 31, 2025 as part of its annual report on Form 10-K covering that period. The information contained in this paragraph, as well as Exhibit 99.1…

Corporate Controller — Lisa M. White: The departure of the Corporate Controller was immediately followed by the appointment of a named internal successor, indicating an orderly succession rather than a sudden loss of leadership.

Other Events. On November 14, 2025, Columbia Banking System, Inc., parent company of Columbia Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.37 per common share, representing a 3% increase to the most recent Columbia dividend declaration. The dividend is payable December 15, 2025, to shareholders of record as of November 28, 2025. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its ent…

CFO — Ivan Seda: The filing discloses the internal promotion of Ivan Seda to CFO and the orderly transition of the outgoing CFO, Ronald L. Farnsworth, into a senior advisor role, which constitutes a succession event rather than a sudden loss of executive leadership.

Results of Operations and Financial Condition. On October 30, 2025, Columbia Banking System, Inc. issued a press release announcing third quarter 2025 financial results. The release is attached hereto as Exhibit 99.1. Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended September 30, 2025 as part of its quarterly report on Form 10-Q covering that period. The information contained in this paragraph, as well as Exhibit 99.1 referenc…

Director — Steven R. Gardner: The filing discloses the appointment of former Pacific Premier directors to Columbia's board and a consulting agreement for the former CEO following a merger, which constitutes a succession and integration event rather than a sudden loss of a sitting executive.

Completion of Acquisition or Disposition of Assets. The information set forth in the Introductory Note of this Current Report on Form 8-K is incorporated by reference into this

Other Events. On August 15, 2025, Columbia Banking System, Inc., parent company of Columbia Bank, 1 announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.36 per common share. The dividend is payable September 15, 2025, to shareholders of record as of August 29, 2025. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Regulation FD Disclosure. Columbia Banking System, Inc. (“Columbia”) and Pacific Premier Bancorp, Inc. (“Pacific Premier”) issued a joint press release on August 6, 2025 announcing that all requisite regulatory approvals have been obtained for the previously announced all-stock transaction in which Columbia will acquire Pacific Premier in a series of mergers (the “Merger”) pursuant to the Agreement and Plan of Merger (the “Merger Agreement”), dated as of April 23, 2025, by and among Columbia,…

Results of Operations and Financial Condition. On July 24, 2025, Columbia Banking System, Inc. issued a press release announcing second quarter 2025 financial results. The release is attached hereto as Exhibit 99.1. The information included in the press release is considered to be "furnished" under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended June 30, 20…

Other Events. On May 16, 2025, Columbia Banking System, Inc., parent company of Umpqua Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.36 per common share. The dividend is payable June 16, 2025, to shareholders of record as of May 30, 2025. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Entry into a Material Definitive Agreement On April 23, 2025, Columbia Banking System, Inc., a Washington corporation (“Columbia”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Pacific Premier Bancorp, Inc., a Delaware corporation (“Pacific Premier”), and Balboa Merger Sub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Columbia (“Merger Sub”). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therei…

Results of Operations and Financial Condition. On April 23, 2025, Columbia Banking System, Inc. issued a press release announcing first quarter 2025 financial results. The release is attached hereto as Exhibit 99.1. The information included in the press release is considered to be "furnished" under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended March 31, 2…

Executive Chair — Cort O'Haver: The Executive Chair role was eliminated upon successful completion of the Umpqua merger integration, and the director was replaced by an existing board member (Maria Pope) in an orderly succession.

Regulation FD Disclosure. As previously disclosed by Columbia Banking System, Inc. (the “Company”) in its periodic reports including its Annual Report on Form 10-K for the year ended December 31, 2024 filed with the Securities and Exchange Commission on February 25, 2025, in August 2020 a class action complaint was filed in the United States District Court (ND Cal) alleging aiding and abetting claims against the Company’s bank subsidiary, Umpqua Bank (the “Bank”). The claims were associated w…

Other Events. On February 14, 2025, Columbia Banking System, Inc., parent company of Umpqua Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.36 per common share. The dividend is payable March 17, 2025, to shareholders of record as of February 28, 2025. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Results of Operations and Financial Condition. On January 23, 2025, Columbia Banking System, Inc. issued a press release announcing fourth quarter and full year 2024 financial results. The release is attached hereto as Exhibit 99.1. The information included in the press release is considered to be "furnished" under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Columbia Banking System, Inc. will include final financial statements and additional analyses for the year end…

Other Events. On November 15, 2024, Columbia Banking System, Inc., parent company of Umpqua Bank, announced its Board of Directors has approved a quarterly cash dividend in the amount of $0.36 per common share. The dividend is payable December 16, 2024, to shareholders of record as of November 29, 2024. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference in its entirety.

Results of Operations and Financial Condition. On October 24, 2024, Columbia Banking System, Inc. issued a press release announcing third quarter 2024 financial results. The release is attached hereto as Exhibit 99.1. The information included in the press release is considered to be "furnished" under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Columbia Banking System, Inc. will include final financial statements and additional analyses for the quarter ended September…