M. Christian Mitchell - 31 Aug 2025 Form 4 Insider Report for COLUMBIA BANKING SYSTEM, INC. (COLB)

Role: Director
Signature: /s/ Lisa M. White, Attorney-in-fact
Issuer symbol: COLB
Transactions as of: 31 Aug 2025
Net transactions value: $0
Form type: 4
Filing time: 03 Sep 2025, 21:31:11 UTC
Previous filing: 14 Aug 2025
Next filing: 02 Oct 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
MITCHELL M CHRISTIAN	Director	C/O COLUMBIA BANKING SYSTEM, INC., 1301 A STREET, TACOMA	/s/ Lisa M. White, Attorney-in-fact	03 Sep 2025	0001284574

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	COLB	Common Stock	Award	$0	+35,755		$0.000000	35,755	31 Aug 2025	Direct	F1
transaction	COLB	Common Stock	Award	$0	+2,205	+6.2%	$0.000000	37,960	02 Sep 2025	Direct	F2

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Acquired in connection with Columbia Banking System, Inc.'s ("Columbia") acquisition of Pacific Premier Bancorp, Inc. ("Pacific Premier") on August 31, 2025. Pursuant to the merger agreement, each issued and outstanding share of Pacific Premier common stock held by the reporting person was converted into the right to receive 0.9150 of a share of Columbia common stock. All fractional share holdings were paid in cash. On August 29, 2025, the closing price of Columbia common stock was $26.77, and the closing price of Pacific Premier common stock was $24.49.
F2	Restricted stock awards that vest in their entirety on May 15, 2026.

Content

Acquired in connection with Columbia Banking System, Inc.'s ("Columbia") acquisition of Pacific Premier Bancorp, Inc. ("Pacific Premier") on August 31, 2025. Pursuant to the merger agreement, each issued and outstanding share of Pacific Premier common stock held by the reporting person was converted into the right to receive 0.9150 of a share of Columbia common stock. All fractional share holdings were paid in cash. On August 29, 2025, the closing price of Columbia common stock was $26.77, and the closing price of Pacific Premier common stock was $24.49.

Restricted stock awards that vest in their entirety on May 15, 2026.