144 0001634415 XXXXXXXX LIVE 0001835830 KLAVIYO, INC 001-41806 125 SUMMER ST, 6TH FLOOR BOSTON MA 02110 617-213-1788 Summit Partners Growth Equity Fund IX-A, L.P. 10% Stockholder Series A Common stock, par value $0.001 per share Goldman Sachs & Co. LLC

200 West Street New York NY 10282

2955112 54255856.32 126937933 08/11/2026 NYSE Series A common stock, par value $0.001 per share 09/20/2023 Pre-IPO Transactions Klaviyo, Inc. N 32170006 09/20/2023 Equity interests in the Issuer were purchased pre-IPO. Y 08/11/2026 Adam Hennessey