Notice of Proposed Sale · 144

Klaviyo, Inc.

KVYONYSEEQUITYCurrent

Notice of Proposed Sale

Filed Sep 24, 2026Accepted Sep 24, 2026, 4:12 PM EDTFiling CIK 1991125Accession 0001959173-26-007106

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Structured filing — 144

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Notice of proposed sale. The proposed amounts below do not establish that a sale occurred.

Proposed-sale notice

Issuer: Klaviyo, Inc.
Issuer CIK: 0001835830
SEC file number: 001-41806
Phone: 800-338-1744
Person for whose account securities are to be sold: Hallen Ed
Relationships to issuer: Officer · Director
Street: 125 SUMMER STREET, FLOOR 6
City: BOSTON
State / country code: MA
Postal code: 02110

Securities proposed for sale

Securities proposed for sale · 1 reported row
Security	Proposed units	Aggregate market value	Units outstanding	Approximate sale date	Exchange	Broker / market maker
Class A	1,300	22,124.00	126,937,933	09/24/2026	NYSE	Fidelity Brokerage Services LLC

Broker / market maker — proposed row 1, entry 1

Name: Fidelity Brokerage Services LLC
Street: 900 Salem Street
City: Smithfield
State / country code: RI
Postal code: 02917

Acquisition of securities to be sold

Acquisition of securities to be sold · 1 reported row
Security	Acquired	Nature of acquisition	Acquired from	Amount acquired	Gift transaction	Payment date	Nature of payment
Class A	09/25/2012	Founders Shares	Issuer	1,300	N	09/25/2012	Compensation

Sales reported in the preceding three months

Sales reported in the preceding three months · 2 reported rows
Seller	Security	Sale date	Amount sold	Gross proceeds
Hodgkins Llc	Class A	08/31/2026	59,615	1,221,349.02
Hodgkins Trust	Class A	08/31/2026	39,167	801,622.32

Seller — prior-sale row 1, entry 1

Name: Hodgkins Llc
Street: 125 Summer Street
Street (continued): 6th Floor
City: Boston
State / country code: MA
Postal code: 02110

Seller — prior-sale row 2, entry 1

Name: Hodgkins Trust
Street: 125 Summer Street
Street (continued): 6th Floor
City: Boston
State / country code: MA
Postal code: 02110

Prior-sale reporting

Nothing to report for the preceding three months: N

Remarks

Today's sale includes 800 shares sold from Hodgkins Llc, of which Edward W Hallen is an authorized individual and account stakeholder; and 500 shares sold from Hodgkins Trust, of which Edward W. Hallen is an account stakeholder.

Notice signature

Notice date: 09/24/2026
Signed: /s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Edward Hallen
Plan adoption dates: 06/01/2026

Company context

Current securities

KVYONYSE · EQUITY · Current

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