Summit Partners discloses 12.03% beneficial ownership in Klaviyo

Rhea-AI Filing Summary

Summit Partners-affiliated funds filed Amendment No. 5 to Schedule 13G reporting their beneficial ownership in Klaviyo, Inc. (KVYO). The group reports an aggregate 12.03% of Klaviyo’s Series A Common Stock, calculated based on 137,856,147 Series A shares outstanding as of October 31, 2025, plus 18,852,778 Series A shares issuable upon conversion of their Series B shares.

The reported securities are held across several entities, including Fund IX-A with 11,142,414 Series A shares issuable (7.11%) and Fund IX-B with 6,957,168 issuable (4.44%), alongside smaller positions by Kiwi Co-Invest, Fund IX/VC IV, and Fund IX/VC IV (UK). Voting and dispositive powers are reported as shared in amounts corresponding to each fund’s position. The filing notes that certain principals may be deemed to share authority, while all parties disclaim beneficial ownership beyond their direct holdings.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 5)

Klaviyo, Inc.

(Name of Issuer)

Series A Common Stock, par value $0.001 per share

(Title of Class of Securities)

49845K101

(CUSIP Number)

09/30/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Partners Growth Equity Fund IX-A, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 11,142,414.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 11,142,414.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

11,142,414.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.11 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Represents 11,142,414 shares of Series A Common Stock ("Series A Shares") issuable in respect of 11,142,414 shares of Series B Common Stock ("Series B Shares"). Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's Quarterly Report on Form 10-Q (the "10-Q") filed with the Securities and Exchange Commission ("SEC") on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Partners Growth Equity Fund IX-B, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 6,957,168.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 6,957,168.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

6,957,168.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

4.44 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Represents 6,957,168 Series A Shares issuable in respect of 6,957,168 Series B Shares. Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Partners Co-Invest (Kiwi), L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 687,035.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 687,035.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

687,035.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.44 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Represents 687,035 Series A Shares issuable in respect of 687,035 Series B Shares. Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Investors GE IX/VC IV, LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 58,561.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 58,561.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

58,561.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.04 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: Represents 58,561 Series A Shares issuable in respect of 58,561 Series B Shares. Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Investors GE IX/VC IV (UK), L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 7,600.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 7,600.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

7,600.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

0.01 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Represents 7,600 Series A Shares issuable in respect of 7,600 Series B Shares. Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

CUSIP No. 49845K101

1

Names of Reporting Persons

Summit Partners, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 18,852,778.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 18,852,778.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

18,852,778.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

12.03 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: Represents 18,852,778 Series A Shares issuable in respect of 18,852,778 Series B Shares. Calculated based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders (as defined in Item 2).

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Klaviyo, Inc.
(b)	Address of issuer's principal executive offices: 125 Summer Street, Floor 6, Boston, MA 02110
Item 2.
(a)	Name of person filing: This statement is filed by the entities and persons listed below, all of whom together are referred to herein as the "Reporting Persons": (i) Summit Partners Growth Equity Fund IX-A, L.P. ("Fund IX-A") (ii) Summit Partners Growth Equity Fund IX-B, L.P. ("Fund IX-B") (iii) Summit Partners Co-Invest (Kiwi), L.P. ("Kiwi Co-Invest Fund") (iv) Summit Investors GE IX/VC IV, LLC ("Fund IX/VC IV") (v) Summit Investors GE IX/VC IV (UK), L.P. ("Fund IX/VC IV (UK)," and together with each of the foregoing, the "Summit Holders") (vi) Summit Partners, L.P.
(b)	Address or principal business office or, if none, residence: 222 Berkeley Street, 18th Floor Boston, MA 02116
(c)	Citizenship: See responses to Item 4 on each cover page.
(d)	Title of class of securities: Series A Common Stock, par value $0.001 per share
(e)	CUSIP No.: 49845K101
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: See responses to Item 9 on each cover page. The aggregate Series A Shares beneficially owned by the Reporting Persons and reflected in this statement represents 12.03% of the outstanding Series A Shares. Such calculation is based upon 137,856,147 Series A Shares outstanding as of October 31, 2025 as reported on the Issuer's 10-Q filed with the SEC on November 5, 2025, as increased by an aggregate of 18,852,778 Series A Shares issuable in respect of the 18,852,778 Series B Shares held by the Summit Holders. In this regard, the reported securities are directly held by Fund IX-A (11,142,414 Series A Shares issuable in respect of 11,142,414 Series B Shares), Fund IX-B (6,957,168 Series A Shares issuable in respect of 6,957,168 Series B Shares), Kiwi Co-Invest Fund (687,035 Series A Shares issuable in respect of 687,035 Series B Shares), Fund IX/VC IV (58,561 Series A Shares issuable in respect of 58,561 Series B Shares), and Fund IX/VC IV (UK) (7,600 Series A Shares issuable in respect of 7,600 Series B Shares). Summit Partners, L.P. is the manager of Summit Partners GE IX, LLC, which is the general partner of Summit Partners GE IX, L.P., which is the general partner of Fund IX-A and 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 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 Fund IX/VC IV and the general partner of Fund IX/VC IV (UK). Summit Master Company, LLC, as the managing member of Summit Investors Management, LLC, has delegated voting and investment decisions with respect to the Series B Shares held by Fund IX/VC IV and Fund IX/VC IV (UK) to Summit Partners, L.P. The investment committee of Summit Partners, L.P. is currently composed of Peter Chung, Scott Collins and Peter 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 reported securities (except to the extent such securities are directly held by such entity). The filing of this statement shall not be construed as an admission that the Reporting Persons or any of the foregoing are the beneficial owners of any of the securities covered by this statement.
(b)	Percent of class: See responses to Item 11 on each cover page
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: See responses to Item 5 on each cover page.
	(ii) Shared power to vote or to direct the vote: See responses to Item 6 on each cover page.
	(iii) Sole power to dispose or to direct the disposition of: See responses to Item 7 on each cover page.
	(iv) Shared power to dispose or to direct the disposition of: See responses to Item 8 on each cover page.
Item 5.	Ownership of 5 Percent or Less of a Class.
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.	Certifications:
	Not Applicable

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Summit Partners Growth Equity Fund IX-A, L.P.

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Summit Partners Growth Equity Fund IX-B, L.P.

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Summit Partners Co-Invest (Kiwi), L.P.

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Summit Investors GE IX/VC IV, LLC

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Summit Investors GE IX/VC IV (UK), L.P.

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Summit Partners, L.P.

Signature:	/s/ Adam H. Hennessey, as POA
Name/Title:	Adam H. Hennessey, as Power of Attorney
Date:	11/13/2025

Comments accompanying signature: Exhibit A Joint Filing Agreement, dated as of January 31, 2024, incorporated by reference to the Schedule 13G filed by the Reporting Persons on January 31, 2024 Exhibit B Powers of Attorney, incorporated herein by reference to of the statement on Schedule 13G filed by the Reporting Persons on January 31, 2024

FAQ

What stake in Klaviyo (KVYO) do Summit Partners-affiliated funds report?

They report an aggregate 12.03% beneficial ownership of Klaviyo’s Series A Common Stock, based on shares outstanding as of October 31, 2025 plus shares issuable upon conversion.

How many shares underpin the Summit Partners group’s reported position in KVYO?

The position reflects 18,852,778 Series A shares issuable upon conversion of an equal number of Series B shares held by the reporting entities.

What are the largest individual fund positions disclosed for KVYO?

Fund IX-A: 11,142,414 Series A shares issuable (7.11%). Fund IX-B: 6,957,168 Series A shares issuable (4.44%).

What reference share count did the filing use for KVYO?

It uses 137,856,147 Series A shares outstanding as of October 31, 2025, as reported in Klaviyo’s Form 10‑Q filed on November 5, 2025.

Do the reporting persons have shared voting and dispositive power?

Yes. Each fund reports shared voting and shared dispositive power in amounts matching its respective shares issuable.

Which other affiliated vehicles hold KVYO shares in the filing?

Additional holders include Kiwi Co‑Invest (687,035), Fund IX/VC IV (58,561), and Fund IX/VC IV (UK) (7,600), each as Series A shares issuable.