JANA Partners Management, LP filed Amendment No. 5 to its Schedule 13D with the SEC on November 10, 2026, disclosing updated beneficial ownership and an antitrust filing related to its stake in Mercury Systems Inc.

Key Highlights

  • Beneficial ownership: JANA Partners Management, LP reported beneficial ownership of 3,880,671 shares of Mercury Systems Inc. common stock, representing approximately 6.4% of shares outstanding.
  • Aggregate purchase price: The 3,880,671 shares were acquired at an aggregate purchase price of approximately $118 million, according to the filing.
  • Shares outstanding basis: The 6.4% figure is based on 60,863,586 shares outstanding as of September 1, 2026, as reported in the issuer's proxy statement filed September 17, 2026.
  • HSR filing: On November 10, 2026, JANA filed for early termination under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, citing the pending expiration of an existing antitrust clearance.
  • No dispute claimed: The filing states the HSR filing "is not related to any disagreement or dispute with the Issuer, its management, or the Board on any matter relating to the Issuer's operations, policies, or practices."
  • DSUs included: The reported share total includes 9,542 deferred stock units granted to Mr. Ostfeld for board service, of which 7,194 have vested and 2,348 were granted on October 28, 2026.
  • No recent transactions: According to the filing, no transactions in the shares were effected by the Reporting Person during the past 60 days.

JANA Partners Updates Mercury Systems Stake and Discloses HSR Filing

JANA Partners Management, LP, a Delaware-organized investment adviser, filed Amendment No. 5 to its Schedule 13D on November 10, 2026, amending Items 3, 4, and 5(a)-(c) of its original Schedule 13D first filed with the SEC on September 22, 2022. The amendment pertains to common stock of Mercury Systems Inc., par value $0.01 per share, with CUSIP number 589378108. Mercury Systems Inc. is headquartered at 50 Minuteman Road, Andover, Massachusetts 01810, according to the filing.

The filing discloses that JANA's 3,880,671 shares were acquired using investment fund assets and margin borrowings. Those shares are held in commingled margin accounts, which may extend margin credit subject to applicable federal margin regulations, stock exchange rules, and credit policies. The positions held in those accounts are pledged as collateral for debit balances. Because other securities are also held in the margin accounts, the filing states it is not possible to determine the amounts, if any, of margin used to purchase the reported shares.

Regarding the HSR antitrust filing, JANA stated it acted "in light of the pending expiration of an existing antitrust clearance." The beneficial ownership total includes 9,542 deferred stock units held by Mr. Ostfeld in connection with his board service. The 2,348 DSUs granted on October 28, 2026, will vest on the earlier of the first anniversary of the grant date or the next annual meeting of shareholders. Mr. Ostfeld has assigned all rights to any shares issuable under the grant to JANA Partners Management, LP. JANA holds sole voting and dispositive power over all 3,880,671 shares, with no shared voting or dispositive power reported.

What Was Disclosed

JANA Partners Management, LP filed Amendment No. 5 to its Schedule 13D disclosing 3,880,671 shares of Mercury Systems Inc. common stock (approximately 6.4%), an aggregate purchase price of approximately $118 million, an HSR early termination filing, and updated details on deferred stock units held by Mr. Ostfeld.