colb-20260625

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

___________________________________________________

FORM 11-K

___________________________________________________

(Mark One)


x			ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended DECEMBER 31, 2025


[ ]			TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to .

Commission File Number.....000-20288

___________________________________________________

A. Full title of the plan and the address of the plan, if different from that of the issuer named below:

Columbia Bank 401(k) and Profit Sharing Plan

B. Name of issuer of the securities held pursuant to the plan and the address of its principal executive office:

Columbia Banking System, Inc.

1301 A Street

Tacoma, Washington 98402-2156

REQUIRED INFORMATION

1. Not Applicable

2. Not Applicable

3. Not Applicable

4. The Columbia Bank 401(k) and Profit Sharing Plan (the Plan) is subject to the requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). Furnished herewith are the financial statements and schedules of the Plan for the fiscal year ended December 31, 2025, prepared in accordance with the financial reporting requirements of ERISA.

Columbia Bank 401(k) and Profit Sharing Plan

Financial Statements as of December 31, 2025 and 2024, and for the Year Ended December 31, 2025,

Supplemental Schedule as of December 31, 2025,

and Reports of Independent Registered Public Accounting Firms

CONTENTS


		PAGE
REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM		1
REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM		2

FINANCIAL STATEMENTS
	Statements of net assets available for benefits as of December 31, 2025 and 2024	3
	Statement of changes in net assets available for benefits for the year ended December 31, 2025	4
	Notes to financial statements as of December 31, 2025 and 2024, and for the year ended December 31, 2025	5

SUPPLEMENTAL INFORMATION REQUIRED BY THE DEPARTMENT OF LABOR
	Schedule H, Part IV, Line 4(i) – Schedule of assets (held at end of year) as of December 31, 2025	12


INDEX TO EXHIBITS
	EXHIBITS 23.1 - Consent of Independent Registered Public Accounting Firm	13
	EXHIBITS 23.2 - Consent of Independent Public Accounting Firm	13

SIGNATURES		14

NOTE:
	All other schedules required by Section 2520.103-10 of the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974 have been omitted because they are not applicable.

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Plan Participants and Plan Administrator of

Columbia Bank 401(k) and Profit Sharing Plan

Opinion on the Financial Statements

We have audited the accompanying statement of net assets available for benefits of the Columbia Bank 401(k) and Profit Sharing Plan (the "Plan") as of December 31, 2025, the related statement of changes in net assets available for benefits for the year ended December 31, 2025, and the related notes and schedules (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2025, and the changes in net assets available for benefits for the year ended December 31, 2025, in conformity with accounting principles generally accepted in the United States of America ("U.S.").

Basis for Opinion

These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on the Plan’s financial statements based on our audit. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) ("PCAOB") and are required to be independent with respect to the Plan in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Plan is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audit, we are required to obtain an understanding of internal control over financial reporting, but not for the purpose of expressing an opinion on the effectiveness of the Plan’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audit included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audit also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audit provides a reasonable basis for our opinion.

Supplemental Information

The supplemental information contained in Schedule H, Part IV, Line 4(i) - Schedule of Assets (Held at End of Year) as of December 31, 2025 has been subjected to audit procedures performed in conjunction with the audit of the Plan's financial statements. The supplemental information is the responsibility of the Plan's management. Our audit procedures included determining whether the supplemental information reconciles to the financial statements or the underlying accounting and other records, as applicable, and performing procedures to test the completeness and accuracy of the information presented in the supplemental information. In forming our opinion on the supplemental information, we evaluated whether the supplemental information, including its form and content, is presented in conformity with the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. In our opinion, the supplemental information is fairly stated, in all material respects, in relation to the financial statements as a whole.

/s/ Aprio, LLP

We have served as the Plan’s auditor since 2025 (such date takes into account the acquisition of the attest business of Delap LLP by Aprio, LLP effective January 1, 2026).

Lake Oswego, Oregon

June 25, 2026

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Plan Participants and Plan Administrator of the

Umpqua Bank 401(k) and Profit Sharing Plan

Opinion on the Financial Statements

We have audited the accompanying statement of net assets available for benefits of the Umpqua Bank 401(k) and Profit Sharing Plan (the "Plan") as of December 31, 2024 and the related notes and schedules (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2024, in conformity with accounting principles generally accepted in the United States of America ("U.S.").

Basis for Opinion

/s/ Delap LLP

We began serving as the Plan’s auditor in 2025.

Lake Oswego, Oregon

June 27, 2025

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS

DECEMBER 31, 2025 and 2024


				December 31,
(in thousands)				2025		2024
ASSETS
	Investments, at fair value			$	836,653	$	749,453








	Receivables
		Notes receivable from participants		12,219		11,162
		Employer contributions - match		744		709

		Participant contributions		270		4
		Unsettled trades		3		—
			Total receivables	13,236		11,875

NET ASSETS AVAILABLE FOR BENEFITS				$	849,889	$	761,328

See accompanying notes.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS

YEAR ENDED DECEMBER 31, 2025


(in thousands)				2025
ADDITIONS TO NET ASSETS ATTRIBUTED TO
	Investment income
		Net appreciation in fair value of investments		$	108,228
		Dividends		10,808
		Interest		30

			Net investment income	119,066

	Interest income on notes receivable from participants			938

	Contributions
		Employer		13,442
		Participant		37,765
		Rollovers		9,637

			Total contributions	60,844

			Total additions	180,848

DEDUCTIONS FROM NET ASSETS ATTRIBUTED TO

	Benefits paid to participants			91,654
	Corrective distributions			26
	Administrative expenses			607

			Total deductions	92,287

CHANGE IN NET ASSETS				88,561




NET ASSETS AVAILABLE FOR BENEFITS
	Beginning of year			761,328
	End of year			$	849,889

See accompanying notes.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 1 – Description of Plan

The following description of the Columbia Bank 401(k) and Profit Sharing Plan (the "Plan") provides only general information. Participants should refer to the Plan Agreement, as amended, for a more complete description of Plan provisions. Effective September 1, 2025, the Plan's name changed from Umpqua Bank 401(k) and Profit Sharing Plan in connection with the Company's transition to a unified "Columbia Bank" brand.

General – The Plan is a 401(k) salary deferral and profit sharing plan covering substantially all employees of Columbia Banking System, Inc. and Subsidiaries (the Company), and is subject to provisions of the Employee Retirement Income Security Act of 1974, as amended (ERISA). The Company is the Plan's sponsor and serves as Plan administrator.

Eligibility – All employees, except those employees who are (1) residing in Puerto Rico, (2) covered by a collective bargaining agreement, unless the collective bargaining agreement specifically provides for participation in the Plan, (3) a nonresident alien with no income from a U.S. source, or (4) not common-law employees, such as leased employees and individuals designated as independent contractors, are eligible to participate in the 401(k) portion of the Plan upon reaching age 18. Once the eligibility criteria have been met, employees are automatically enrolled into the Plan at a deferral rate of 6% of their eligible compensation, unless they choose to opt-out. Employees enter the Plan on scheduled enrollment dates following their completion of the eligibility requirements.

Contributions – Contributions are subject to regulatory limitations.

Employee deferrals – Participants may elect to contribute up to 80% of eligible compensation. In addition, participants may make voluntary Roth after-tax contributions or voluntary non-deductible after-tax contributions to the Plan. Participants may also roll over eligible amounts from other qualified plans. Participants who have attained age 50 before the end of the Plan year are eligible to make catch-up contributions.

Employer match – The Company may elect to make discretionary matching contributions to the Plan. Matching contributions are made each pay period. The Company matched 50% of employee contributions, up to 8% of eligible compensation deferred to the Plan for the year ended December 31, 2025.

Employer profit sharing – The Company may elect to make discretionary profit sharing contributions to the Plan. Participants must complete at least 1,000 hours of service during the Plan year and be employed as of the last day of the Plan year, to be eligible to receive any profit sharing contributions. Profit sharing contributions are allocated to participants in the same proportion as a participant's compensation bears to the total of all participants' compensation. There were no profit sharing contributions for the year ended December 31, 2025.

Participant accounts – Each participant's account is credited with the participant's contribution and allocations of the Company's contributions and Plan earnings, and charged with an allocation of administrative expenses. Allocations are based on participant earnings or account balances, as defined. Participants direct the investment of their account balances into various investment options offered by the Plan. The Plan currently offers various registered investment company mutual funds, Company common stock, and common trusts, as investment options for participants. Previously, self-directed brokerage accounts were also available to participants. However, in 2023 the Plan was updated to disallow new accounts and prevent investment updates to existing self-directed brokerage accounts.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 1 – Description of Plan (continued)

Vesting – Participants are fully vested at all times in that portion of their accounts attributable to their own contributions and earnings or losses thereon. Vesting in Company contributions is based on years of service pursuant to the following vesting schedule. Participants who were part of acquired plans may have specific vesting schedules in accordance with those plans.



Years of service		Percentage
	Less than 1 year	—%
	1 year but less than 2	20%
	2 years but less than 3	40%
	3 years but less than 4	60%
	4 years but less than 5	80%
	5 years or more	100%

Notes receivable from participants – Participants may borrow from their accounts a minimum of $1,000 up to 50% of the participant's vested account, but not in excess of $50,000. Loans are secured by the balance of the participant's account and bear fixed, reasonable rates of interest, as determined by the Plan administrator. The maximum loan term is five years unless the loan qualifies as a home loan. Principal and interest are paid ratably through payroll deductions. As of December 31, 2025, the rates of interest on outstanding loans ranged from 3.25% to 9.50% with various maturities through 2047.

Payment of benefits – On termination of service due to death, disability, or retirement, a participant may elect to receive a lump-sum amount equal to the value of the participant's vested interest in his or her account balance, or annual installments over a period not more than the participant's life expectancy (or the assumed life expectancies of the participant and their beneficiary). For termination of service for other reasons, a participant may receive the value of the vested interest in their account as a lump-sum, fixed amount, fixed amount over time, withdrawal based on life expectancy, or fixed percentage withdrawal distribution.

Hardship withdrawals of the participants' contributions are permitted by the Plan. Hardship withdrawals must be approved by the Plan administrator and are limited to vested amounts of participants' contributions.

Note 2 – Summary of Significant Accounting Policies

Basis of accounting – The financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, using the accrual method of accounting.

Use of estimates – The preparation of financial statements in conformity with generally accepted accounting principles requires the use of estimates and assumptions that may affect certain reported amounts and disclosures. Accordingly, actual results could differ from those estimates.

Investment valuation – Investments are stated at fair value. Fair value is the price that would be received to sell an asset or paid to transfer a liability (i.e., the "exit price") in an orderly transaction between market participants at the measurement date. See Note 3 for discussion of fair value measurements.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 2 – Summary of Significant Accounting Policies (continued)

Notes receivable from participants – Notes receivable from participants are measured at amortized cost, which represents unpaid principal balance plus accrued but unpaid interest. Interest income is recorded on the accrual basis. Delinquent notes receivable from participants are recorded as distributions based on the terms of the Plan Agreement.

Income recognition – Purchases and sales of securities are recorded on a trade-date basis. Dividends are recorded on the ex-dividend date. Interest income is recorded on the accrual basis. The net appreciation in fair value of investments consists of both the realized gains or losses and unrealized depreciation and appreciation of those investments.

Payment of benefits – Benefit payments are recorded when paid.

Contributions – Contributions are recognized during the period in which the respective payroll deductions are made. Employer and Participant contributions are invested directly in appropriate funds based upon Participant elections made at the date of enrollment or through authorized changes in elections.

Expenses – Administrative expenses such as legal and accounting fees are paid by the Company; however, they may be paid with Plan forfeitures. Transaction fees and investment management fees are deducted directly from the participant's account.

Forfeitures – Forfeitures are the nonvested portion of a participant's account that are lost upon termination of employment. Forfeitures are retained in the Plan and will be used to reduce future Company contributions, and eligible, reasonable administrative expenses. As of December 31, 2025 and 2024, forfeited non-vested accounts totaled $661,000 and $288,000, respectively. During 2025, the Company used $779,000 of forfeitures to fund 2025 matching contributions.

Subsequent events – Subsequent events are events or transactions that occur after the statement of net assets available for benefits date but before financial statements are issued. The Plan recognizes in the financial statements the effects of all subsequent events that provide additional evidence about conditions that existed at the date of the statement of net assets available for benefits, including the estimates inherent in the process of preparing the financial statements. The Plan's financial statements do not recognize subsequent events that provide evidence about conditions that did not exist at the date of the statement of net assets available for benefits but arose after the statement of net assets available for benefits date and before financial statements were issued.

Note 3 – Fair Value Measurements

The fair value framework provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurement) and the lowest priority to unobservable inputs (level 3 measurements).

The asset or liability's fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques maximize the use of observable inputs and minimize the use of unobservable inputs.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 3 – Fair Value Measurements (continued)

The following is a description of the valuation methodologies used for assets measured at fair value.

Money markets and other cash equivalents – Valued at quoted market prices, which represent the net asset value (NAV) of shares held by the Plan at year end. Money market and other cash equivalents are generally classified within level 1 of the valuation hierarchy.

Registered investment companies (mutual funds) – Valued at quoted market prices, which represent the NAV of shares held by the Plan at year end. Mutual funds are generally classified within level 1 of the valuation hierarchy.

Common stock – Valued at the closing price reported on the active market on which the individual securities are traded. Common stock is generally classified within level 1 of the valuation hierarchy.

Self-directed brokerage – The self-directed brokerage accounts include money markets, mutual funds, and common stock, which are valued within the brokerage account using level 1 valuation inputs.

Collective trusts – Units held in collective trusts are valued using the NAV of the funds. The NAV is used as a practical expedient to estimate fair value. The NAV is based on the fair value of the underlying assets owned by the fund, minus its liabilities, and then divided by the number of units outstanding. Participant transactions (purchases and sales) may occur daily at NAV. Investments in collective investment funds are redeemable daily at NAV, which is the readily determinable fair value. The common collective trust funds measured at NAV have not been classified in the fair value hierarchy.

The Plan invests in fourteen collective investment trusts, twelve of which are target date funds for investors expecting to retire around the year indicated in each fund's name. The price per share is quoted on a private market that is not active. One of the remaining collective trusts that the Plan invests in is the Putnam Stable Value Fund 15, which is designed to provide preservation of capital and achieve high current income through a diversified portfolio. The fund invests primarily in security-backed investment contracts issued by insurance companies and other financial institutions, fixed income securities, and money market funds. The remaining collective trust that the Plan invests in is the Cohen & Steers U.S. Realty Fund Class RS, which seeks to maximize total return by outperforming its benchmark, FTSE Nareit All Equity REITs Index, over the long term. The fund invests in a diversified portfolio of common stocks of real estate companies and other permitted investments. It invests in publicly traded real estate companies that own income-producing properties or land, including real estate investment trusts (REITs) and real estate corporations, primarily domiciled in the United States.

The valuation methods used by the Plan may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, although the Plan believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 3 – Fair Value Measurements (continued)

The following tables disclose by level, the fair value hierarchy, of the Plan's assets at fair value:


		Investment Assets at Fair Value as of December 31, 2025
(in thousands)		Level 1		Level 2		Level 3		Total

Money markets and other cash equivalents		$	176	$	—	$	—	$	176
Registered investment companies		379,666		—		—		379,666
Common stock - Columbia Banking System, Inc.		15,070		—		—		15,070
Self-directed brokerage accounts		2,645		—		—		2,645
	Total assets in the fair value hierarchy	$	397,557	$	—	$	—	$	397,557
Investments measured at NAV (1)
	Collective trusts							$	439,096

Total investments at fair value								$	836,653

(1)	Certain investments that were measured at net asset value per share have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the statement of net assets available for benefits.


		Investment Assets at Fair Value as of December 31, 2024
(in thousands)		Level 1		Level 2		Level 3		Total

Money markets and other cash equivalents		$	60	$	—	$	—	$	60
Registered investment companies		344,389		—		—		344,389
Common stock – Columbia Banking System, Inc.		15,200		—		—		15,200
Self-directed brokerage accounts		4,387		—		—		4,387
	Total assets in the fair value hierarchy	$	364,036	$	—	$	—	$	364,036
Investments measured at NAV (1)
	Collective trusts							$	385,417



Total investments at fair value								$	749,453

(1)	Certain investments that were measured at net asset value per share have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the statement of net assets available for benefits.

The following tables summarize investments for which fair value is measured using the NAV per share practical expedient:

December 31, 2025

Fair Value

Unfunded Commitments

Redemption Frequency

Redemption Notice Period

(in thousands)

Collective trusts

439,096

None

Daily

N/A

December 31, 2024

Fair Value

Unfunded Commitments

Redemption Frequency

Redemption Notice Period

(in thousands)

Collective trusts

385,417

None

Daily

N/A

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

NOTES TO FINANCIAL STATEMENTS

AS OF DECEMBER 31, 2025 AND 2024, AND FOR THE YEAR ENDED DECEMBER 31, 2025

Note 4 – Tax Status

The Internal Revenue Service (IRS) has determined and informed the Company by a letter dated June 30, 2020, that the Plan and related trust are designed in accordance with applicable sections of the Internal Revenue Code (IRC). Although the Plan has been amended since receiving the determination letter, the Company and Plan management believe that the Plan is designed and is currently being operated in compliance with the applicable requirements of the IRC, and the Plan and related trust continue to be tax-exempt.

Note 5 – Risks and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks, such as interest rate, market volatility, and credit risk. It is reasonably possible that, given the level of risk associated with investment securities, changes in the near term could materially affect a participant's account balance and the amounts reported in the financial statements.

Note 6 – Related Party Transactions and Exempt Party-in-Interest Transactions

Plan investments include shares of Columbia Banking System, Inc. stock, which is the common stock of the Company. As of December 31, 2025, the Plan's investment in the Company's common stock was $15.1 million, compared to $15.2 million as of December 31, 2024. Certain Plan investments are shares of mutual funds managed by Fidelity Trust Management Company, which is the trustee of the Plan. These transactions qualify as exempt party-in-interest transactions.

Note 7 – Plan Termination

Although it has not expressed any intention to do so, the Company has the right to terminate the Plan and discontinue its contributions at any time. If the Plan is terminated, amounts allocated to a participant's account would become fully vested.

Note 8 – Subsequent Events

On August 31, 2025, the Company completed its all-stock acquisition of Pacific Premier Bancorp, Inc. ("Pacific Premier"), the parent company of Pacific Premier Bank, National Association. In connection with the Company's acquisition of Pacific Premier, the Company assumed a 401(k) plan covering former employees of Pacific Premier. As of January 1, 2026, the Pacific Premier 401(k) plan merged with the Columbia Bank 401(k) and Profit Sharing Plan. This resulted an increase in net assets of $141.3 million as a result of the transfer of assets.

SUPPLEMENTAL INFORMATION

REQUIRED BY THE DEPARTMENT OF LABOR

COLUMBIA BANK 401(k) AND PROFIT SHARING PLAN

EIN: 91-1422237

PLAN NO. 001

SCHEDULE H, PART IV, LINE 4(i) – SCHEDULE OF ASSETS (HELD AT END OF YEAR)

DECEMBER 31, 2025

(a)

(b) Identity of Issue, Borrower, Lessor, or Similar Party

(d) Cost

(e) Current Value

(in thousands)

Vanguard Target 2040

Collective trust

64,582

Vanguard Target 2045

Collective trust

62,899

Vanguard Target 2030

Collective trust

62,053

Vanguard Target 2035

Collective trust

54,889

Vanguard Target 2050

Collective trust

43,415

Vanguard Target 2025

Collective trust

42,978

Vanguard Target 2055

Collective trust

31,753

Putnam Stable Value Fund 15

Collective trust

29,419

Vanguard Target 2020

Collective trust

19,158

Vanguard Target Inc

Collective trust

9,031

Vanguard Target 2060

Collective trust

8,335

Cohen & Steers U.S. Realty Fund Class RS

Collective trust

5,284

Vanguard Target 2065

Collective trust

4,469

Vanguard Target 2070

Collective trust

831

Total collective trusts

439,096

Fidelity 500 Index Fund

Registered investment company

95,122

Fidelity Blue Chip Growth Fund Class K6

Registered investment company

64,208

Vanguard Value Index Fund Institutional Shares

Registered investment company

31,508

Vanguard Mid-Cap Value Index Fund Admiral Shares

Registered investment company

30,181

T. Rowe Price Diversified Mid-Cap Growth Fund I Class

Registered investment company

29,011

Fidelity Small Cap Index Fund

Registered investment company

26,225

Fidelity Total International Index Fund

Registered investment company

17,826

Dodge & Cox Income Fund Class X

Registered investment company

15,567

T. Rowe Price Capital Appreciation Fund I Class

Registered investment company

13,635

Dodge & Cox International Stock Fund Class X

Registered investment company

13,006

Fidelity Mid Cap Index Fund

Registered investment company

12,951

Fidelity U.S. Bond Index Fund

Registered investment company

7,456

BlackRock High Yield Bond Portfolio Class K

Registered investment company

7,265

Vanguard International Growth Fund Admiral Shares

Registered investment company

6,312

Fidelity Inflation-Protected Bond Index Fund

Registered investment company

5,810

John Hancock Small Cap Core Fund Class R6

Registered investment company

3,583

Total registered investment companies

379,666

Vanguard Federal Money Market Fund Investor Shares

Money market fund

176

Columbia Banking System, Inc.

Common stock

15,070

BrokerageLink accounts

Various investments, including registered investment companies, common stocks, money market funds and cash

2,645

Participant loans

3.25% – 9.50%, various maturities through 2047

$—

12,219

848,872

* Indicates party-in-interest

** Information is not required as investments are participant directed.

See accompanying Report of Independent Registered Public Accounting Firm.

INDEX TO EXHIBITS

Exhibit No. Description

23.1 Consent of Independent Registered Public Accounting Firm

23.2 Consent of Independent Public Accounting Firm

SIGNATURES

Pursuant to the requirements of the Securities and Exchange Act of 1934, the Plan Administrator has duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.


						Columbia Bank 401(k) and Profit Sharing Plan

Date: June 25, 2026

						/s/ Brock Lakely
						Brock Lakely
						Executive Vice President, Chief Accounting Officer and Corporate Controller