SEC Form POSASR filed by Integral Ad Science Holding Corp.

As filed with the Securities and Exchange Commission on December 23, 2025

No. 333-271763

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1

TO

FORM S-3

REGISTRATION STATEMENT NO. 333-271763

UNDER

THE SECURITIES ACT OF 1933

Integral Ad Science Holding Corp.

(Exact name of registrant as specified in its charter)

12 E 49th Street, 20th Floor

New York, NY 10017

(646) 278-4871

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

 Lisa Utzschneider

Chief Executive Officer

12 E 49th Street, 20th Floor

New York, NY 10017

(646) 278-4871

(Name, address, including zip code, and telephone number, including area code, of agent for service)

With a copy to:

Russell L. Leaf

Jared N. Fertman

Willkie Farr & Gallagher LLP

787 Seventh Avenue

New York, NY 10019

(212) 728-8000

Approximate date of commencement of proposed sale to the public: Not applicable

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☒

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

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This Post-Effective Amendment No. 1 (this “Post-Effective Amendment”) is being filed by Integral Ad Science Holding Corp., a Delaware corporation (the “Registrant”), to deregister all securities remaining unsold under the following Registration Statement on Form S-3 (the “Registration Statement”) filed by the Registrant with the U.S. Securities and Exchange Commission (the “SEC”):

On December 23, 2025, pursuant to the terms of the Agreement and Plan of Merger, dated as of September 24, 2025 (the “Merger Agreement”), by and among the Registrant, Igloo Group Parent, Inc., a Delaware corporation (“Parent”), and Igloo Group Acquisition Company, Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), Merger Sub merged with and into the Registrant, with the Registrant surviving as a wholly owned subsidiary of Parent (the “Merger”).

As a result of the consummation of the transactions contemplated by the Merger Agreement, the Registrant has terminated all offers and sales of its securities registered pursuant to its existing registration statements under the Securities Act of 1933, as amended, including the Registration Statement. In accordance with the undertakings made by the Registrant in the Registration Statement to remove from registration by means of a post-effective amendment any of the securities that had been registered which remain unsold at the termination of the offering, the Registrant, by filing this Post-Effective Amendment, hereby terminates the effectiveness of the Registration Statement and removes and withdraws from registration any and all securities registered but unsold under the Registration Statement as of the date hereof. The Registration Statement is hereby amended, as appropriate, to reflect the deregistration of such securities.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, State of New York, on December 23, 2025.

No other person is required to sign this Post-Effective Amendment in reliance on Rule 478 under the Securities Act of 1933, as amended.

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