Sec Form 4 Filing - Hallen Ed @ Klaviyo, Inc. - 2025-09-15

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Hallen Ed 2. Issuer Name and Ticker or Trading Symbol Klaviyo, Inc. [ KVYO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O KLAVIYO, INC. 125 SUMMER STREET, 6TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/15/2025 (Street) BOSTON, MA02110 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Series A Common Stock 09/15/2025 S( 1 ) 22,224 D $ 31.65 ( 2 ) 177,776 I By Hodgkins Trust ( 3 ) Series A Common Stock 09/15/2025 S( 1 ) 67,524 D $ 31.73 ( 4 ) 722,476 I By Hodgkins LLC ( 5 ) Series A Common Stock 09/15/2025 G( 6 ) 20,260 D $ 0 702,216 I By Hodgkins LLC ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Hallen Ed C/O KLAVIYO, INC. 125 SUMMER STREET 6TH FLOOR BOSTON, MA02110 X X Signatures /s/ Landon Edmond, Attorney-in-Fact 09/17/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )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. ( 2 )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. ( 3 )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. ( 4 )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. ( 5 )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. ( 6 )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.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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