144 0001639368 XXXXXXXX LIVE 0001835830 Klaviyo, Inc. 001-41806 125 Summer Street, 6th Floor Boston MA 02110 6172131788 STEPHEN ROWLAND Officer Common Morgan Stanley Smith Barney LLC Executive Financial Services

1 New York Plaza 8th Floor New York NY 10004

7105 173646.20 116897730 10/15/2025 NYSE Common 08/15/2025 Restricted Stock Units Issuer N 7105 08/15/2025 N/A N 10b5-1 Sales for STEPHEN ROWLAND

125 Summer Street, 6th Floor Boston MA 02110

Common 09/15/2025 7105 226542.59 10b5-1 Sales for STEPHEN ROWLAND

125 Summer Street, 6th Floor Boston MA 02110

Common 08/18/2025 7105 223528.27 10/15/2025 11/22/2024 /s/ Stephen Rowland