X0609 4 2026-09-14 0 0000887343 COLUMBIA BANKING SYSTEM, INC. COLB 0001133099 MACHUCA LUIS false C/O COLUMBIA BANKING SYSTEM, INC. 1301 A STREET TACOMA WA 98402 1 0 0 0 0 Deferred Compensation Phantom Stock 2026-09-14 4 A 0 594 30.48 A Common 594 49560 I Deferred Compensation The deferred compensation plan phantom stock was accrued under the Registrant's deferred compensation plan and will be settled in accordance with the terms of the deferred compensation plan following the reporting person's cessation of service as a director of the Registrant. /s/ Kumi Yamamoto Baruffi, Attorney-in-fact 2026-09-15