The U.S. Securities and Exchange Commission is requiring activist investors to publicly identify their clients in regulatory filings — a surprise move that could significantly disrupt the hedge fund industry, which has long fought to keep such information private.
The updated guidance, covering 13D filings and proxy statements, was issued by the nation’s top securities regulator on Thursday. Legal advisers who work in investor activism said the changes were unexpected and had not been widely anticipated. Those attorneys spoke anonymously in order to discuss the matter candidly.
The new guidance falls under the SEC’s Corporate Finance Interpretations and clarifies how the agency applies its rules to key filings. The update comes after a particularly active six-month stretch of activist investor campaigns. The regulator did not respond to requests for comment and has not explained what prompted the timing of the new interpretation.
Attorneys who advise on these matters say the changes reflect a growing interest in making investor activity more transparent — especially regarding what investors pushing for corporate changes must reveal about who is backing them. The guidance arrives as so-called “sidecar” special purpose vehicles have become an increasingly popular tool for financing activist campaigns.
In addressing Question 110.09, the SEC states: “The identities of the investors in an entity formed for the purpose of acquiring securities of a specific issuer and engaging in an activism campaign at that issuer must be disclosed.”
The agency also addressed Question 155.02, which asks whether clients count as “participants” in a limited partnership seeking to solicit votes for changes to a company’s board of directors. The SEC’s answer is yes — if those clients invested more than $500.
The first half of 2026 saw a surge in activist investing, with firms including Elliott Investment Management, Ancora Alternatives, and TOMS Capital Investment Management pressuring companies such as media giant Warner Bros Discovery and Devon Energy to improve their performance.
Hedge funds have traditionally guarded the identities of their investors closely, arguing that revealing such information could invite copycat strategies and hurt their ability to generate returns. As these funds compete to attract more capital, many have turned to special purpose vehicles that allow individual clients to invest in specific companies rather than participate in a broader fund pool.
Companies on the receiving end of activist campaigns, however, have argued that knowing who is behind those efforts is essential information for mounting a defense.
The SEC’s new stance is likely to bring back memories of a 2022 episode involving medical device company Masimo Corp. Facing a campaign by Politan Capital, Masimo updated its bylaws to require any activist seeking to nominate directors to disclose the identities of the fund’s limited partners and reveal any future plans to nominate candidates at other companies.
That move drew sharp backlash from experienced activist investors. While few other companies followed Masimo’s example, hundreds of corporations reached out to their attorneys to explore whether similar bylaw changes made sense for them, according to legal advisers. By early 2023, Masimo reversed course and dropped the disclosure requirement. The company was later acquired by Danaher in 2026.
