COLUMBIA BANKING SYSTEM INC

Insider Trading Arrangements and Policies

A significant portion of the compensation of our executive officers is delivered in the form of equity awards, including time-vested restricted stock unit awards, and time-vested stock awards that vest ratably over three-year periods, and performance-based restricted stock unit awards. that typically vest over a three-year performance period. This compensation design is intended to align executive compensation with the performance experienced by our shareholders. Following the delivery of shares of our common stock under those equity awards, once any applicable service-, time- or performance-based vesting standards have been satisfied, our executive officers from time to time engage in the open-market sale of some of those shares. Certain of our officers have elected to have shares withheld at the time of vesting to cover withholding taxes.

Our directors and executive officers may also engage from time to time in other transactions involving our securities. Transactions in our securities by our directors and executive officers are required to be made in accordance with our Insider Trading and Information Policy, which, among other things, requires that the transactions be in accordance with applicable U.S. federal securities laws that prohibit trading while in possession of material non-public information. Rule 10b5-1 under the Exchange Act provides an affirmative defense that enables pre-arranged transactions in securities in a manner that avoids concerns about initiating transactions at a future date while possibly in possession of material non-public information. Our Insider Trading and Information Policy permits our directors and executive officers to enter into trading plans designed to comply with Rule 10b5-1.

On December 3, 2024, Torran Nixon, Senior Executive Vice President of the Company, adopted a trading arrangement for the sale of shares of stock (a “Rule 10b5-1 Trading Plan”) that is intended to satisfy the affirmative defense conditions of Exchange Act Rule 10b5-1(c). Mr. Nixon's Rule 10b5-1 Trading Plan provides for termination on March 7, 2025 (subject to earlier termination for certain customary termination events) and for the sale of up to 7,461 shares of common stock.

During the year ended December 31, 2024, other than disclosed above, 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 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 designed 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).

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

Columbia entered into Participation Agreements (the "Participation Agreements") with Christopher Merrywell and Torran Nixon (each a "Named Executive"), on February 24, 2025 and February 25, 2025, respectively, pursuant to the newly adopted Columbia Banking System, Inc. Executive Change in Control and Severance Plan (the "Plan"). The Participation Agreements are effective upon expiration of existing arrangements for Mr. Merrywell and Mr. Nixon 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 Form of Participation Agreement, which is included as Exhibit 10.81 to this Annual Report on Form 10-K and is incorporated by reference.