Form 3 Filing by Simone Lagomarsino

This filing reports initial ownership of securities by Simone Lagomarsino, who is a director at COLUMBIA BANKING SYSTEM, INC. (COLB). The filing indicates that Lagomarsino holds 32,931 shares of common stock indirectly through a family trust and 7 shares indirectly through an IRA. The reporting period was September 1, 2026, and the signature date was September 2, 2026. The filing is an initial statement of beneficial ownership.