Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * Atlas Venture Fund VIII, L.P. 2. Issuer Name and Ticker or Trading Symbol INTEGRAL AD SCIENCE HOLDING CORP. [IAS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 56 WAREHAM STREET, FLOOR 3 3. Date of Earliest Transaction (Month/Day/Year) 12/23/2025 (Street) BOSTON, MA 02118 4. If Amendment, Date Original Filed (Month/Day/Year) 6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _X_ 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 (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 Common stock, $0.001 par value 12/23/2025 J(1) 22,722,770 D $10.3(1) 0 I See Footnote(2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Atlas Venture Fund VIII, L.P. 56 WAREHAM STREET, FLOOR 3 BOSTON, MA 02118		X
Atlas Venture Associates VIII, L.P. 56 WAREHAM STREET, FLOOR 3 BOSTON, MA 02118		X
Atlas Venture Associates VIII, Inc. 56 WAREHAM STREET, FLOOR 3 BOSTON, MA 02118		X

Signatures

Atlas Venture Fund VIII, L.P., By: Atlas Venture Associates VIII, L.P., its general partner, By: Atlas Venture Associates VIII, Inc., its general partner, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci		12/23/2025
**Signature of Reporting Person		Date
Atlas Venture Associates VIII, L.P. By: Atlas Venture Associates VIII, Inc., its general partner, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci		12/23/2025
**Signature of Reporting Person		Date
Atlas Venture Associates VIII, Inc, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci		12/23/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	This Form 4 reports securities disposed pursuant to the Agreement and Plan of Merger, dated as of September 24, 2025 (the "Merger Agreement") by and among the Issuer, 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"). Pursuant to the Merger Agreement, on December 23, 2025 (the "Effective Time"), Merger Sub merged with and into the Issuer, with the Issuer surviving as a wholly owned subsidiary of Parent. At the Effective Time, each share of common stock of the Issuer owned by the reporting persons immediately prior to the Effective Time was automatically cancelled, extinguished and converted into the right to receive $10.30 in cash, without interest thereon.
(2)	Shares held directly by Atlas Venture Fund VIII, L.P. ("Atlas VIII"). Atlas Venture Associates VIII, L.P. ("AVA VIII LP") is the sole general partner of Atlas VIII. Atlas Venture Associates VIII, Inc. ("AVA VIII Inc.") is the sole general partner of AVA VIII LP. Each of Atlas VIII, AVA VIII LP and AVA VIII Inc. disclaim beneficial ownership of all shares except to the extent of its pecuniary interest, if any, therein. This report shall not be deemed to be an admission that the reporting persons are the beneficial owners of such securities for purposes of Section 16 or for any other purpose.

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