[Form 4] Klaviyo, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Andrew Bialecki, CEO and director of Klaviyo, Inc. (KVYO), reported transactions dated 09/23/2025. The filing notes the acquisition of 211,358 shares of Series A Common Stock pursuant to conversion of Series B Common Stock and the sale of 181,553 shares at a weighted average price of $35.52 (sales priced between $35.025 and $36.02) plus an additional sale of 29,805 shares at a weighted average price of $35.01 (sales priced between $35.00 and $35.02). The transactions were effected under a Rule 10b5-1 trading plan adopted May 20, 2025. Footnotes identify several trust holdings for which the reporting person disclaims beneficial ownership except to the extent of pecuniary interest.

Positive

• Sales executed under a Rule 10b5-1 trading plan, which documents pre-arranged trading and reduces concerns about opportunistic timing
• Acquisition via conversion of 211,358 Series B into Series A shares clearly disclosed with conversion mechanics explained

Negative

• Insider sold a total of 211,358 shares on 09/23/2025, which is a sizable disposition by an executive
• Sales occurred at mid-$30s prices (weighted averages $35.52 and $35.01), potentially increasing share supply in the market that day

Insights

Financial Analyst

TL;DR: Significant insider sales occurred under a pre-established 10b5-1 plan; net effect is a large block moved at mid-$30s prices.

The report shows the CEO executed multiple sales totaling 211,358 shares on 09/23/2025 at weighted average prices in the low $35 range, while also recording an acquired position of 211,358 Series A shares from conversion of Series B stock. Because the sales were made pursuant to a 10b5-1 plan adopted May 20, 2025, timing likely follows a pre-set schedule rather than discretionary trading. The disclosed volumes are meaningful relative to an individual insider position and could influence near-term float and supply, though the filing does not state total outstanding shares or percentage ownership to assess exact market impact.

Corporate Governance Expert

TL;DR: Transactions are documented and accompanied by standard trust disclaimers; 10b5-1 adoption reduces governance concerns about opportunistic timing.

The filing clearly states the trades were executed pursuant to a Rule 10b5-1 plan, which is a governance best practice for pre-planned insider sales. The report also discloses multiple trust arrangements and contains standard disclaimers regarding Section 16 beneficial ownership. There is no indication in the filing of any amendment, acceleration, or exceptions to the plan, and no allegations or regulatory flags are present in this document.

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

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

1. Name and Address of Reporting Person^*

Bialecki Andrew

(Last) (First) (Middle)

C/O KLAVIYO, INC.

125 SUMMER STREET, 6TH FLOOR

(Street)

BOSTON MA 02110

(City) (State) (Zip)

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

3. Date of Earliest Transaction (Month/Day/Year)
09/23/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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	09/23/2025		C(1)		211,358	A	(2)	211,358	D
Series A Common Stock	09/23/2025		S(1)		181,553	D	$35.52(3)	29,805	D
Series A Common Stock	09/23/2025		S(1)		29,805	D	$35.01(4)	0	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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (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: 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)	09/23/2025		C(1)			211,358	(2)	(2)	Series A Common Stock	211,358	$0	74,593,469	D
Series B Common Stock	(2)							(2)	(2)	Series A Common Stock	7,517,410		7,517,410	I	By The Andrew P. Bialecki Grantor Retained Annuity Trust I of 2023(5)
Series B Common Stock	(2)							(2)	(2)	Series A Common Stock	517,006		517,006	I	By The Elizabeth L. Bialecki Irrevocable GST Trust of 2023(6)
Series B Common Stock	(2)							(2)	(2)	Series A Common Stock	517,006		517,006	I	By The Andrew P. Bialecki Irrevocable GST Trust of 2023(7)
Series B Common Stock	(2)							(2)	(2)	Series A Common Stock	43,218		43,218	I	By spouse

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 May 20, 2025.

2. 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.

3. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $35.025 to $36.02 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.

4. The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $35.00 to $35.02 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 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.

6. 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.

7. Shares held by the Andrew P. Bialecki Irrevocable GST Trust of 2023, of which the Reporting Person's 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.

Remarks:

	/s/ Landon Edmond, Attorney-in-Fact	09/25/2025
	** Signature of Reporting Person	Date
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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What transactions did Andrew Bialecki report on Form 4 for KVYO?

The filing reports the acquisition of 211,358 Series A shares (via Series B conversion) and sales of 181,553 shares at a weighted average of $35.52 plus 29,805 shares at a weighted average of $35.01, all dated 09/23/2025.

Were the trades by the Klaviyo CEO part of a pre-arranged plan?

Yes. The transactions were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on May 20, 2025.

What price ranges were disclosed for the sales in the Form 4?

The filing discloses sales priced between $35.025 and $36.02 for one block and between $35.00 and $35.02 for the other; weighted averages reported are $35.52 and $35.01 respectively.

Does the Form 4 indicate any indirect holdings or trust arrangements?

Yes. Footnotes disclose shares held by multiple trusts including the Andrew P. Bialecki Grantor Retained Annuity Trust I of 2023 and irrevocable GST trusts, with standard disclaimers about Section 16 beneficial ownership.

When was the Form 4 signed and filed?

The signature block shows an attorney-in-fact executed the filing on 09/25/2025.