Sec Form 3 Filing - Bialecki Andrew @ Klaviyo, Inc. - 2023-09-20

FORM 3 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 Bialecki Andrew 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 X __ Officer (give title below) _____ Other (specify below) Chief Executive Officer (Last) (First) (Middle) C/O KLAVIYO, INC., 125 SUMMER STREET, 6TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/20/2023 (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

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 Series B Common Stock ( 1 ) ( 1 ) ( 1 ) Series A Common Stock 60,359,000 D Series B Common Stock ( 1 ) ( 1 ) ( 1 ) Series A Common Stock 16,000,000 I By The Andrew P. Bialecki Grantor Retained Annuity Trust I of 2023 ( 2 ) Series B Common Stock ( 1 ) ( 1 ) ( 1 ) Series A Common Stock 517,006 I By The Andrew P. Bialecki Irrevocable GST Trust of 2023 ( 3 ) Series B Common Stock ( 1 ) ( 1 ) ( 1 ) Series A Common Stock 517,006 I By The Elizabeth L. Bialecki Irrevocable GST Trust of 2023 ( 4 ) Series B Common Stock ( 1 ) ( 1 ) ( 1 ) Series A Common Stock 43,218 I By spouse Stock Option (Right to Buy) $ 0.0125 ( 5 ) 08/31/2025 Series B Common Stock 15,829,184 D Stock Option (Right to Buy) $ 0.0125 ( 5 ) 09/28/2025 Series B Common Stock 5,600,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Bialecki Andrew C/O KLAVIYO, INC. 125 SUMMER STREET, 6TH FLOOR BOSTON, MA02110 X X Chief Executive Officer Signatures /s/ Landon Edmond, Attorney-in-Fact 09/20/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )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 of the Issuer, and will automatically convert into 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. ( 2 )Shares held by the Andrew P. Bialecki Grantor Retained Annuity Trust I of 2023, of which the Reporting Person serves as trustee. 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. ( 3 )Shares held by the Andrew P. Bialecki Irrevocable GST Trust of 2023, of which the Reporting Persons spouse serves as a trustee. 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 )Shares held by the Elizabeth L. Bialecki Irrevocable GST Trust of 2023, of which the Reporting Person serves as a trustee. 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. ( 5 )The shares underlying this option are fully vested and exercisable as of the date hereof.

Remarks: Exhibit 24 Power of Attorney

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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