Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Series A Common Stock, par value $0.001 per share^F1,F2,F3,F4	Aug 11, 2026	C	5,000,000	—	A	5,000,000	I	See footnotes
Series A Common Stock, par value $0.001 per share^F2,F3,F4	Aug 11, 2026	S	5,000,000	$17.71	D	0	I	See footnotes

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	Owned after	D/I
Series B Common Stock, par value $0.001 per share^{F1,F5,F2,F3,F4}	—	Aug 11, 2026	C	5,000,000	A	—	—	Series A Common Stock, par value $0.001 per share	5,000,000	13,852,778	I

Explanation of responses

F1The Series B common stock, par value $0.001 per share ("Series B Common Stock"), is convertible into an equal number of shares of Series A common stock, par value $0.001 per share ("Series A Common Stock"), at any time, at the holder's election, and has no expiration date. Each share of Series B Common Stock will automatically convert into Series A Common Stock upon the earlier of (i) the date specified by 66-2/3% of the outstanding shares of Series B Common Stock, voting as a single series; (ii) following the seventh anniversary of the closing of Klaviyo, Inc.'s (the "Company") initial public offering; or (iii) any transfer, whether or not for value, except for certain permitted transfers described in the Company's certificate of incorporation.
F2Summit Partners, L.P. is the manager of Summit Partners GE IX, LLC, which is the general partner of Summit Partners GE IX, LP, which is the general partner of Summit Partners Growth Equity Fund IX-A, L.P. ("Fund IX-A") and Summit Partners Growth Equity Fund IX-B, L.P. ("Fund IX-B"). Summit Partners, L.P. is the managing member of Summit Partners Co-Invest Kiwi GP, LLC, which is the general partner of Summit Partners Co-Invest (Kiwi), L.P. ("Kiwi Co-Invest Fund"). Summit Master Company, LLC is the general partner of Summit Partners, L.P., which is the manager of Summit Investors Management, LLC, which is the manager of Summit Investors GE IX/VC IV, LLC ("Fund IX/VC IV") and the general partner of Summit Investors GE IX/VC IV (UK), L.P. ("Fund IX/VC IV (UK)").
F3(continued from footnote 2) Summit Master Company, LLC, as the managing member of Summit Investors Management, LLC, has delegated voting and investment decisions with respect to the securities held by Fund IX/VC IV and Fund IX/VC IV (UK) to Summit Partners, L.P.
F4The investment committee of Summit Partners, L.P., is currently composed of Peter Y. Chung, Scott C. Collins, and Peter L. Rottier, who may be deemed to have voting and dispositive authority over, and therefore beneficial ownership of, the reported securities. Each of the foregoing entities, Mr. Chung, Mr. Collins, and Mr. Rottier disclaims beneficial ownership of the shares, except to the extent of such person's or entity's pecuniary interest therein and the filing of this statement shall not be deemed an admission that any of the foregoing entities or persons are, for purposes of Section 16 of the Act or otherwise, the beneficial owner of any equity securities covered by this statement.
F5Consists of (i) 8,187,302 shares of Series B Common Stock held by Fund IX-A, (ii) 5,112,037 shares of Series B Common Stock held by Fund IX-B, (iii) 504,825 shares of Series B Common Stock held by Kiwi Co-Invest Fund, (iv) 43,030 shares of Series B Common Stock held by Fund IX/VC IV, and (v) 5,584 shares of Series B Common Stock held by Fund IX/VC IV (UK).