COLUMBIA BANKING SYSTEM, INC.

Rule 10b5-1 or Non-Rule 10b5-1 Trading Arrangements

During the second quarter of 2025 none of our directors or officers adopted orterminated a trading plan intended to satisfy Rule 10b5-1 or any "non-Rule 10b5-1 trading arrangement," as defined in Item 408 of Regulation S-K.

Certain of our officers and directors have made elections to participate in, and are participating in, our 401(k) and profit sharing plan and have made, and may from time to time make, elections to (i) have shares withheld to cover withholding taxes or (ii) have dividends from Columbia common stock reinvested into Columbia common stock, (iii) have a portion of their 401(k) account contributions used to purchase Columbia common stock, or (iv) participate in the employee stock purchase plan, which may be intended to satisfy the affirmative defense conditions of Rule 10b5-1 under the Exchange Act or may constitute non-Rule 10b5-1 trading arrangements (as defined in Item 408(c) of Regulation S-K).

Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year

On August 4, 2025, the Board of Directors of the Company amended and restated the Company's Amended and Restated Bylaws to remove certain corporate governance provisions that were added to the Company's Amended and Restated Bylaws in connection with the Umpqua Merger (the "Amendment"). The Amendment removed provisions from the Company's Amended and Restated Bylaws related to (i) the roles of the Company's Chief Executive Officer and former Executive Chair, and (ii) the headquarters and name of the Company and the Bank.

The foregoing summary of the Amendment does not purport to be complete and is qualified in its entirety by reference to the full text of the Amended and Restated Bylaws of the Company, a copy of which is attached hereto as Exhibit 3.2 to this Quarterly Report on Form 10-Q and is incorporated herein by reference.