144 0001991125 XXXXXXXX LIVE 0001835830 Klaviyo, Inc. 001-41806 125 SUMMER STREET, FLOOR 6 BOSTON MA 02110 800-338-1744 Hallen Ed Officer Director Series A Fidelity Brokerage Services LLC

900 Salem Street Smithfield RI 02917

59492 1787420.89 137856147 11/10/2025 NYSE Series A 09/25/2012 Founder Shares Issuer N 59492 09/25/2012 Compensation N Hodgkins Llc

125 Summer Street, 6th Floor Boston MA 02110

Series A 09/15/2025 67524 2142377.45 Hodgkins Trust

125 Summer Street, 6th Floor Boston MA 02110

Series A 09/15/2025 22224 703493.05 Of the shares sold today, 8,572 shares were sold in the Hodgkins Trust, of which Edward W. Hallen is an account stakeholder and 50,920 shares were sold in the Hodgkins Llc, of which Edward W. Hallen is an authorized individual and an account stakeholder. There are trades on 09/15/2025 which also occurred in Hodgkins Trust, and Hodgkins Llc. 11/10/2025 06/12/2025 /s/ Gary Redman, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Edward W. Hallen