Sec Form 3 Filing - Whalen Amanda @ 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 Whalen Amanda 2. Issuer Name and Ticker or Trading Symbol Klaviyo, Inc. [ KVYO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Financial 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 Series A Common Stock 200,000 ( 1 ) D

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 ( 2 ) ( 2 ) ( 2 ) Series A Common Stock 742,542 ( 3 ) D

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

Explanation of Responses:

( 1 )Consists of restricted stock units (RSUs) awarded under the 2023 Stock Incentive Plan, each representing the contingent right to receive one share of Series A Common Stock upon vesting and settlement. The RSUs vest as follows: 32% of the RSUs vest in four equal quarterly installments beginning on November 15, 2023, 27% of the RSUs will vest in four equal quarterly installments beginning on November 15, 2024, 18% of the RSUs will vest in four equal quarterly installments beginning on November 15, 2025, and the remaining 23% of the RSUs will vest in four equal quarterly installments beginning on November 15, 2026, subject to the Reporting Persons continued service on each such vesting date. ( 2 )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. ( 3 )Amount consists of (a) 120,667 shares of Series B Common Stock and (b) 621,875 unvested RSUs awarded under the 2015 Stock Incentive Plan, each representing the contingent right to receive one share of Series B Common Stock upon vesting and settlement. The RSUs vest as follows: (i) 378,125 RSUs vest in eleven equal quarterly installments through May 15, 2026 and (ii) 81,250 RSUs vest in equal quarterly installments through February 15, 2025, with the remaining 162,500 RSUs vesting in four equal quarterly installments thereafter, subject to the Reporting Person's continued service on each such vesting date.

Remarks: Exhibit 24 Power of Attorney

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