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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(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 13D/A 0001998597 XXXXXXXX LIVE 3 Common Stock, par value $0.01 per share 11/06/2025 false 0001049521 589378108 MERCURY SYSTEMS INC 50 Minuteman Road Andover MA 01810 Ele Klein & Adriana Schwartz 212-756-2000 McDermott Will & Schulte LLP 919 Third Avenue New York NY 10022 0001998597 N JANA Partners Management, LP AF N DE 4966675.00 0.00 4966675.00 0.00 4966675.00 N 8.3 IA PN Common Stock, par value $0.01 per share MERCURY SYSTEMS INC 50 Minuteman Road Andover MA 01810 This Amendment No. 3 ("Amendment No. 3") amends and supplements the statement on Schedule 13D filed with the SEC on September 22, 2022 (as amended from time to time, the "Schedule 13D") with respect to the Shares of the Issuer. This Amendment No. 3 amends Items 5 and 6 as set forth below. Capitalized terms used herein and not otherwise defined in this Amendment No. 3 have the meanings set forth in the Schedule 13D. Item 5(a) of the Schedule 13D is hereby amended and restated in its entirety as follows: The aggregate percentage of Shares reported to be beneficially owned by the Reporting Person is based upon 60,100,136 Shares outstanding as of October 31, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended September 26, 2025, filed with the SEC on November 4, 2025. As of the close of business on the date hereof, JANA may be deemed to beneficially own 4,966,675 Shares, representing approximately 8.3% of the Shares outstanding. This includes 4,832 deferred stock units ("DSUs") granted to Mr. Ostfeld on October 23, 2024 and 2,362 DSUs granted to Mr. Ostfeld on October 22, 2025, for his service on the Board of Directors of the Issuer (the "Board"). The DSUs vest on the earlier of the first anniversary of the grant date and the next annual meeting of shareholders. Vested DSUs do not convert into Shares until the date on which Mr. Ostfeld ceases to be a member of the Board. Mr. Ostfeld has assigned all rights to any Shares issuable pursuant to the grant to the Reporting Person. Pursuant to the assignment, settlement of the award on vesting will be made to the Reporting Person. Item 5(b) of the Schedule 13D is hereby amended and restated in its entirety as follows: The Reporting Person has sole voting and dispositive power over 4,966,675 Shares, which power is exercised by the Principal. Item 5(c) of the Schedule 13D is hereby amended and restated in its entirety as follows: Information concerning transactions in the Shares effected by the Reporting Person in the past sixty (60) days is set forth in Schedule A hereto and is incorporated herein by reference. All of the transactions in Shares listed therein were effected in the open market through various brokerage entities. In addition, as disclosed in Item 5(a), on October 22, 2025, 2,362 DSUs were granted to Mr. Ostfeld for his service on the Board. Item 6 of the Schedule 13D is hereby amended and supplemented as follows: The information disclosed in Item 5(a) is incorporated herein by reference. JANA Partners Management, LP /s/ Jennifer Fanjiang Jennifer Fanjiang, Partner, Chief Legal Officer and Chief Compliance Officer 11/10/2025