COLUMBIA BANKING SYSTEM INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

SCHEDULE 14A

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a)

of the Securities Exchange Act of 1934 (Amendment No.)

Check the appropriate box:

Preliminary Proxy Statement

Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

Definitive Proxy Statement

Definitive Additional Materials

Soliciting Material Pursuant to §240.14a-12

COLUMBIA BANKING SYSTEM, INC.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

No fee required

Fee paid previously with preliminary material

Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

Columbia Banking System, Inc.

1301 A Street

Tacoma, Washington 98402-4200

April 3, 2025

To our Shareholders:

It has been two years since completion of the merger of Columbia Banking System, Inc. ("Columbia") and Umpqua Holdings

Corporation ("Umpqua"). With 2024 marking our first full year of combined performance, our Board of Directors (the "Board")

determined to remove certain merger-related provisions from our Bylaws to better reflect the governance of the combined company.

As a result, Columbia’s Bylaws no longer require that the Board be comprised of seven pre-merger Columbia directors and seven

pre-merger Umpqua directors, nor do they require that the Lead Independent Director be a pre-merger Columbia director. In light of

this progress and with the integration comfortably behind us, the Board also determined that the Executive Chair role served by

Cort O'Haver was no longer needed, and his service with the Company concluded on March 31, 2025.

The Board has nominated 11 individuals for re-election at this year’s annual meeting of shareholders, which will be held on

Thursday, May 15, 2025, at 10:00 a.m. Pacific Time. Directors Craig Eerkes and Peggy Fowler have not been nominated due

to their desire to retire from the Columbia Board as of the annual meeting, having served, respectively, as Chair of Columbia’s

Board and Chair of Umpqua’s board of directors prior to the merger closing. Since that time, Mr. Eerkes has served as the Lead

Independent Director of Columbia, and Ms. Fowler has served as the Chair of Columbia’s Nominating and Governance Committee.

Their many years of service and their leadership in our first years of operation as a combined company are deeply appreciated.

The annual meeting on May 15, 2025, will be conducted exclusively via live webcast. We believe this format enables engagement

with our shareholders regardless of size, resources or physical location. You will be able to attend the meeting online, vote your

shares electronically and submit questions during the meeting by visitingwww.virtualshareholdermeeting.com/COLB2025.

To participate in the virtual meeting, you will need the 16-digit control number included on your Notice, proxy card or voting

instruction form. The meeting webcast will begin promptly at 10:00 a.m. Pacific Time. We encourage you to access the meeting

prior to the start time. Online check-in will begin at 9:45 a.m., and you should allow ample time for the check-in procedures. If you

experience any difficulties while accessing the virtual meeting during the check-in or meeting time, a technical assistance phone

number will be made available on the virtual meeting registration page starting at 9:45 a.m. on the date of the meeting.

At the meeting, in addition to voting on the matters set forth in the proxy statement, you will have the opportunity to hear

management discuss developments in our business and industry in the past year and to ask questions pertinent to the meeting.

You will find additional information concerning our company and its operations, including its audited financial statements, in the

Annual Report for the year ended December 31, 2024, which is available on our website atwww.columbiabankingsystem.com

in the “Quarterly Results” section.

Whether or not you plan to attend the virtual meeting, please take the time to vote online, by telephone or by completing

and mailing the proxy card (if you received one) as soon as possible. Your opinion and your vote are important to us. Voting

by proxy will not prevent you from voting online if you attend the meeting, but it will ensure that your vote is counted if you are

unable to attend.

Notice of Annual Meeting of Shareholders

Time and Date

10:00 a.m. Pacific Time on Thursday, May 15, 2025

Virtual Meeting

www.virtualshareholdermeeting.com/COLB2025

How To Participate

Visit www.virtualshareholdermeeting.com/COLB2025 and enter the control number found on your Notice, proxy card or instruction form.

Record Date

You are entitled to vote at the annual meeting and at any adjournments or postponements of the meeting if you were a shareholder at the close of business on March 17, 2025.