144 0001846709 XXXXXXXX LIVE 0001835830 Klaviyo, Inc. 001-41806 125 Summer Street, 6th Floor Boston MA 02110 617-213-1788 SUMMIT INVESTORS GE IX/VC IV (UK), L.P. Owner Series A common stock, par value $0.001 per share Barclays Capital Inc.

745 7th Avenue New York NY 10019

847 34227.27 78803963 12/09/2024 NYSE Series A common stock, par value $0.001 per share 09/20/2023 Pre-IPO transactions. Klaviyo, Inc. N 21945 09/20/2023 Equity interests in the Issuer were purchased pre-IPO. N Summit Investors GE IX/VC IV (UK), L.P.

222 Berkeley St 18th FL Boston MA 02116

Series A common stock, par value $0.001 per share 09/11/2024 2 62.02 Summit Investors GE IX/VC IV (UK), L.P.

222 Berkeley St 18th FL Boston MA 02116

Series A common stock, par value $0.001 per share 09/12/2024 43 1347.25 Summit Investors GE IX/VC IV (UK), L.P.

222 Berkeley St 18th FL Boston MA 02116

Series A common stock, par value $0.001 per share 09/13/2024 46 1447.69 Summit Investors GE IX/VC IV (UK), L.P.

222 Berkeley St 18th FL Boston MA 02116

Series A common stock, par value $0.001 per share 11/14/2024 1411 51078.2 12/09/2024 /s/ Adam Hennessey