COLUMBIA BANKING SYSTEM INC

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

During the third quarter of 2024 none of our directors or officers adopted or terminated 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, 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 November 4, 2024, the board of directors (the “Board”) of the Company amended and restated the Company’s Amended and Restated Bylaws to (i) provide that the number of directors to be elected by the shareholders shall consist of not less than eight nor more than fifteen persons; (ii) remove the requirement that the Lead Independent Director of the Board must be an individual that served on the Board prior to the Merger (a “Continuing Columbia Director"); (iii) remove the requirement that the Board and the board of directors of the Bank be comprised of seven Continuing Columbia Directors and seven individuals that served on the board of directors UHC prior to the Merger for a period of 36 months following the closing of the Merger; and (iv) make certain non-substantive administrative and clarifying updates (clauses (i)‑(iv), collectively, the “Amendments”).

The foregoing summary of the Amendments 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.

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

Columbia entered into Participation Agreements with Aaron Deer and Ron Farnsworth (each a “Named Executive”), on November 5, 2024, pursuant to the newly adopted Columbia Banking System, Inc. Executive Change in Control and Severance Plan. The Participation Agreements are effective upon expiration of existing arrangements for Mr. Farnsworth on January 1, 2025, and for Mr. Deer on March 1, 2025. Under the Plan, if a Named Executive’s employment is terminated by Columbia without Cause or the Named Executive terminates their employment with Columbia for Good Reason following the effective date of the applicable Participation Agreement (as such terms “Cause” and “Good Reason” are defined in the Plan, each a “Qualifying Termination”), in each case not in connection with a change in control, the Named Executive will be entitled to receive, subject to execution and non-revocation of a release of claims, cash severance equal to one year’s base salary. If a Named Executive experiences a Qualifying Termination within six months prior to, or within 24 months following, a change in control, the Named Executive will be entitled to receive, subject to execution and non-revocation of a release of claims, (1) cash severance equal to two times the sum of the Named Executive’s annual base salary and target annual bonus, (2) a prorated target bonus for the year of termination, (3) continued health and welfare benefits for 18 months, and (4) vesting of any outstanding equity awards granted in full with respect to any service vesting requirement, and any awards subject to a performance-vesting condition will remain outstanding and eligible to be earned in full based on the level of performance achieved as if the Named Executive had remained employed for the duration of the performance period. The Named Executives will be subject to customary restrictive covenants, including non-competition and non-solicitation covenants, during employment and for up to two years thereafter.

The foregoing description of the Plan and the Participation Agreements does not purport to be complete and is qualified in its entirety by reference to the full text of the Plan and the Form of Participation Agreement, which are attached hereto as Exhibits 10.1 and 10.2 to this Quarterly Report on Form 10-Q and are incorporated herein by reference.