144 0001733091 XXXXXXXX LIVE 0001835830 Klaviyo, Inc. 001-41806 125 SUMMER STREET, FLOOR 6 BOSTON MA 02110 800-338-1744 Galvin Carmel Officer Series A Fidelity Brokerage Services LLC

900 Salem Street Smithfield RI 02917

11156 389121.28 94683729 05/16/2025 NYSE Series A 05/15/2025 Restricted Stock Vesting Issuer N 11156 05/15/2025 Compensation N Carmel Galvin

125 Summer Street 6th Floor Boston MA 02110

Series A 02/25/2025 11531 465119.78 05/16/2025 11/26/2024 /s/ Gary Redman, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Carmel Galvin