KVYO

SEC source: 0001470831-25-000215 · wk-form4_1758141493.xml · derivative · entry 4

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 74,804,827

Underlying: Series A Common Stock · 226,382 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F5 · balance_after: Reflects 4,428,420 shares of Series B Common Stock previously transferred from the Andrew P. Bialecki Grantor Retained Annuity Trust I of 2023 to the Reporting Person.

SEC source: 0001470831-25-000215 · wk-form4_1758141493.xml · nonDerivative · entry 3

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F4 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.32 to $32.01 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000215 · wk-form4_1758141493.xml · nonDerivative · entry 2

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 85,461

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $32.02 to $33.01 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000215 · wk-form4_1758141493.xml · nonDerivative · entry 1

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 226,382

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000212 · wk-form4_1758140370.xml · nonDerivative · entry 1

Fernandez Gomez Luciano · CIK 0001730978 · Director · Interim Executive Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 127,385

F1 · shares: Represents restricted stock units ("RSUs") awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), upon vesting and settlement. The RSUs vest in full on November 15, 2025, subject to the Reporting Person's continued service on the vesting date.

F2 · balance_after: Consists of (i) 20,968 shares of Series A Common Stock and (ii) 106,417 unvested RSUs awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000210 · wk-form4_1758140127.xml · nonDerivative · entry 2

Rowland Stephen Eric · CIK 0001639368 · President

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 438,621

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 22, 2024.

F3 · balance_after: Consists of (i) 129,070 shares of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and (ii) 309,551 unvested restricted stock units awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000210 · wk-form4_1758140127.xml · nonDerivative · entry 1

Rowland Stephen Eric · CIK 0001639368 · President

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 438,821

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 22, 2024.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.43 to $32.27 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000217 · wk-form4_1758141626.xml · nonDerivative · entry 3

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: Plan reported

Ownership: Indirect · By Hodgkins LLC

Disclosed balance after: 702,216

F6 · kind: Represents a bona fide gift of 20,260 shares of stock from the Reporting Person to a donor-advised fund pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 12, 2025.

F5 · ownership.nature: Shares held by Hodgkins LLC, of which the Reporting Person serves as manager. The Reporting Person disclaims Section 16 beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed to be an admission that he has beneficial ownership of such shares for Section 16 or any other purpose.

SEC source: 0001470831-25-000217 · wk-form4_1758141626.xml · nonDerivative · entry 2

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: Plan reported

Ownership: Indirect · By Hodgkins LLC

Disclosed balance after: 722,476

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 12, 2025.

F4 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.15 to $31.98 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F5 · ownership.nature: Shares held by Hodgkins LLC, of which the Reporting Person serves as manager. The Reporting Person disclaims Section 16 beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed to be an admission that he has beneficial ownership of such shares for Section 16 or any other purpose.

SEC source: 0001470831-25-000217 · wk-form4_1758141626.xml · nonDerivative · entry 1

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: Plan reported

Ownership: Indirect · By Hodgkins Trust

Disclosed balance after: 177,776

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 12, 2025.

F2 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.07 to $31.965 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F3 · ownership.nature: Shares are owned directly by Hodgkins Trust for the benefit of the Reporting Person and the Reporting Person's family, and of which the trustee is an independent institution. The Reporting Person disclaims Section 16 beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed to be an admission that he has beneficial ownership of such shares for Section 16 or any other purpose.

SEC source: 0001470831-25-000197 · wk-form4_1757714997.xml · derivative · entry 3

Whalen Amanda · CIK 0001991131 · Chief Financial Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 408,476

Underlying: Series A Common Stock · 11,204 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on August 16, 2024.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F5 · balance_after: Consists of (i) 224,101 shares of Series B Common Stock and (ii) 184,375 unvested RSUs awarded under the Issuer's 2015 Stock Incentive Plan, each representing the contingent right to receive one share of Series B Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000197 · wk-form4_1757714997.xml · nonDerivative · entry 2

Whalen Amanda · CIK 0001991131 · Chief Financial Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 481,719

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on August 16, 2024.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.17 to $31.98 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F4 · balance_after: Consists of (i) 42,687 shares of Series A Common Stock and (ii) 439,032 unvested restricted stock units ("RSUs") awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000197 · wk-form4_1757714997.xml · nonDerivative · entry 1

Whalen Amanda · CIK 0001991131 · Chief Financial Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 496,719

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on August 16, 2024.

F2 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000196 · wk-form4_1757714934.xml · derivative · entry 5

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 31,999,106

Underlying: Series A Common Stock · 990,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000196 · wk-form4_1757714934.xml · nonDerivative · entry 4

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Indirect · By Hodgkins LLC

Disclosed balance after: 790,000

F2 · kind: On September 11, 2025, the Reporting Person transferred 200,000 shares of Series A Common Stock to Hodgkins Trust and 790,000 shares of Series A Common Stock to Hodgkins LLC for estate planning purposes, in each case for no consideration.

F4 · ownership.nature: Shares held by Hodgkins LLC, of which the Reporting Person serves as manager. The Reporting Person disclaims Section 16 beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed to be an admission that he has beneficial ownership of such shares for Section 16 or any other purpose.

SEC source: 0001470831-25-000196 · wk-form4_1757714934.xml · nonDerivative · entry 3

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Indirect · By Hodgkins Trust

Disclosed balance after: 200,000

F2 · kind: On September 11, 2025, the Reporting Person transferred 200,000 shares of Series A Common Stock to Hodgkins Trust and 790,000 shares of Series A Common Stock to Hodgkins LLC for estate planning purposes, in each case for no consideration.

F3 · ownership.nature: Shares are owned directly by Hodgkins Trust for the benefit of the Reporting Person and the Reporting Person's family, and of which the trustee is an independent institution. The Reporting Person disclaims Section 16 beneficial ownership of such shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed to be an admission that he has beneficial ownership of such shares for Section 16 or any other purpose.

SEC source: 0001470831-25-000196 · wk-form4_1757714934.xml · nonDerivative · entry 2

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

F2 · kind: On September 11, 2025, the Reporting Person transferred 200,000 shares of Series A Common Stock to Hodgkins Trust and 790,000 shares of Series A Common Stock to Hodgkins LLC for estate planning purposes, in each case for no consideration.

SEC source: 0001470831-25-000196 · wk-form4_1757714934.xml · nonDerivative · entry 1

Hallen Ed · CIK 0001991125 · Director · 10% owner

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 990,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000195 · wk-form4_1757714866.xml · nonDerivative · entry 1

St. Ledger Susan · CIK 0001673606 · Director

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 10,939

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 11, 2025.

F2 · balance_after: Consists of (i) 5,119 shares of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and (ii) 5,820 unvested restricted stock units awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000185 · wk-form4_1757621167.xml · derivative · entry 3

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 70,602,789

Underlying: Series A Common Stock · 220,481 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000185 · wk-form4_1757621167.xml · nonDerivative · entry 2

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.44 to $32.345 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000185 · wk-form4_1757621167.xml · nonDerivative · entry 1

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 220,481

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0000950170-25-113988 · ownership.xml · derivative · entry 3

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 18,852,778

Underlying: Series A Common Stock, par value $0.001 per share · 4,000,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: The 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.

F1 · derivative.exercise_date: The 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.

F1 · derivative.expiration_date: The 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.

F5 · balance_after: Consists of (i) 11,142,414 shares of Series B Common Stock held by Fund IX-A, (ii) 6,957,168 shares of Series B Common Stock held by Fund IX-B, (iii) 687,035 shares of Series B Common Stock held by Kiwi Co-Invest Fund, (iv) 58,561 shares of Series B Common Stock held by Fund IX/VC IV, and (v) 7,600 shares of Series B Common Stock held by Fund IX/VC IV (UK).

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0000950170-25-113988 · ownership.xml · nonDerivative · entry 2

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 0

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0000950170-25-113988 · ownership.xml · nonDerivative · entry 1

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnotes

Disclosed balance after: 4,000,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: The 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.

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0001470831-25-000167 · wk-form4_1757016925.xml · derivative · entry 4

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 70,823,270

Underlying: Series A Common Stock · 223,304 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000167 · wk-form4_1757016925.xml · nonDerivative · entry 3

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F4 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $30.61 to $30.87 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000167 · wk-form4_1757016925.xml · nonDerivative · entry 2

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 94,427

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $30.88 to $31.87 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000167 · wk-form4_1757016925.xml · nonDerivative · entry 1

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 223,304

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · derivative · entry 7

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 71,046,574

Underlying: Series A Common Stock · 3,500,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · nonDerivative · entry 5

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F6 · kind: Represents a bona fide gift of 3,500,000 shares of stock from the Reporting Person to a donor-advised fund. The Reporting Person directed the transfer of 3,500,000 shares of their Series B Common Stock, resulting in the automatic conversion of the shares into Series A Common Stock upon execution of the transfer pursuant to the Issuer's certificate of incorporation. These shares remain subject to a lock-up agreement for a period of 60 days following August 13, 2025, as required pursuant to a lock-up agreement the Reporting Person entered into with the underwriter in connection with a registered stock offering.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · nonDerivative · entry 4

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 3,500,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F5 · price: The Reporting Person directed the transfer of 3,500,000 shares of their Series B Common Stock in connection with a bona fide gift to a donor-advised fund, resulting in the automatic conversion of the shares into Series A Common Stock upon execution of the transfer pursuant to the Issuer's certificate of incorporation.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · derivative · entry 6

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 74,546,574

Underlying: Series A Common Stock · 226,702 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · derivative.exercise_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · nonDerivative · entry 3

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 0

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F4 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.17 to $31.22 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · nonDerivative · entry 2

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 10,269

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.225 to $32.22 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

SEC source: 0001470831-25-000156 · wk-form4_1756411727.xml · nonDerivative · entry 1

Bialecki Andrew · CIK 0001991099 · Director · Chief Executive Officer · 10% owner

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 226,702

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 20, 2025.

F2 · price: Each share of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), is convertible at any time at the option of the holder into one share of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001415889-25-023115 · form4-08272025_080802.xml · derivative · entry 3

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 22,852,778

Underlying: Series A Common Stock, par value $0.001 per share · 975,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: The 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.

F1 · derivative.exercise_date: The 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.

F1 · derivative.expiration_date: The 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.

F5 · balance_after: Consists of (i) 13,506,504 shares of Series B Common Stock held by Fund IX-A, (ii) 8,433,272 shares of Series B Common Stock held by Fund IX-B, (iii) 832,803 shares of Series B Common Stock held by Kiwi Co-Invest Fund, (iv) 70,986 shares of Series B Common Stock held by Fund IX/VC IV, and (v) 9,213 shares of Series B Common Stock held by Fund IX/VC IV (UK).

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0001415889-25-023115 · form4-08272025_080802.xml · nonDerivative · entry 2

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 0

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0001415889-25-023115 · form4-08272025_080802.xml · nonDerivative · entry 1

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Summit Partners Co-Invest (Kiwi), LP · CIK 0001830877 · 10% owner

SUMMIT INVESTORS GE IX/VC IV, LLC · CIK 0001654074 · 10% owner

SUMMIT INVESTORS GE IX/VC IV (UK), L.P. · CIK 0001846709 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 975,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: The 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.

F2 · ownership.nature: Summit 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 · ownership.nature: (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.

F4 · ownership.nature: The 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.

SEC source: 0000950170-25-110957 · ownership.xml · nonDerivative · entry 1

SUMMIT PARTNERS L P · CIK 0000830588 · 10% owner

Summit Partners Growth Equity Fund IX-A, L.P. · CIK 0001634415 · 10% owner

Summit Partners Growth Equity Fund IX-B, L.P. · CIK 0001634426 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · kind: Represents a distribution of 307,809 shares of Series A common stock, par value $0.001 per share ("Series A Common Stock") held by Summit Partners Growth Equity Fund IX-A, L.P. ("Fund IX-A") and 192,191 shares of Series A Common Stock held by Summit Partners Growth Equity Fund IX-B, L.P. ("Fund IX-B"), in each case to facilitate bona fide charitable gifts.

F2 · ownership.nature: Summit 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 Fund IX-A and Fund IX-B. The 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.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · derivative · entry 6

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 45,000

Underlying: Series A Common Stock · 11,074 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.exercise_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F7 · balance_after: Consists of 45,000 unvested RSUs awarded under the Issuer's 2015 Stock Incentive Plan, each representing the contingent right to receive one share of Series B Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · nonDerivative · entry 4

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 392,584

F4 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on August 16, 2024.

F5 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.20 to $31.76 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F6 · balance_after: Consists of (i) 113,798 shares of Series A Common Stock and (ii) 278,786 unvested RSUs awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · nonDerivative · entry 3

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 402,549

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000141 · wk-form4_1755650948.xml · nonDerivative · entry 2

Galvin Carmel · CIK 0001733091 · Chief People Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 675,833

F2 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 26, 2024.

F3 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.20 to $32.06 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F4 · balance_after: Consists of (i) 86,858 shares of Series A Common Stock and (ii) 588,975 unvested RSUs awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000140 · wk-form4_1755650858.xml · derivative · entry 6

Rowland Stephen Eric · CIK 0001639368 · President

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 410,496

Underlying: Series A Common Stock · 28,457 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.exercise_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F7 · balance_after: Consists of 410,496 unvested RSUs awarded under the Issuer's 2015 Stock Incentive Plan, each representing the contingent right to receive one share of Series B Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000140 · wk-form4_1755650858.xml · nonDerivative · entry 4

Rowland Stephen Eric · CIK 0001639368 · President

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 445,726

F4 · kind: These transactions were effected by the Reporting Person pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on November 22, 2024.

F5 · price: The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $31.20 to $31.77 per share. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

F6 · balance_after: Consists of (i) 136,175 shares of Series A Common Stock and (ii) 309,551 unvested RSUs awarded under the Issuer's 2023 Stock Option and Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement.

SEC source: 0001470831-25-000140 · wk-form4_1755650858.xml · nonDerivative · entry 3

Rowland Stephen Eric · CIK 0001639368 · President

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 452,831

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · derivative · entry 5

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 56,074

Underlying: Series A Common Stock · 11,426 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F1 · kind: Represents 11,426 shares of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), automatically converted into shares of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), in connection with tax withholding obligations related to the vesting and settlement of restricted stock units ("RSUs").

F2 · derivative.exercise_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

F2 · derivative.expiration_date: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · nonDerivative · entry 2

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 391,475

F3 · kind: Represents shares of Series A Common Stock withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting and settlement of RSUs.

SEC source: 0001470831-25-000139 · wk-form4_1755650660.xml · nonDerivative · entry 1

Edmond Landon · CIK 0001991399 · Chief Legal Officer

10b5-1 filing: Plan reported

Ownership: Direct

Disclosed balance after: 416,170

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: Represents 11,426 shares of the Issuer's Series B Common Stock, par value $0.001 per share ("Series B Common Stock"), automatically converted into shares of the Issuer's Series A Common Stock, par value $0.001 per share ("Series A Common Stock"), in connection with tax withholding obligations related to the vesting and settlement of restricted stock units ("RSUs").

F2 · price: Each share of Series B Common Stock is convertible at any time at the option of the holder into one share of Series A Common Stock and will automatically convert into one share of Series A Common Stock upon the occurrence of certain events as set forth in the Issuer's certificate of incorporation. The Series B Common Stock has no expiration date.