Sio Capital Management, LLC filed a Schedule 13G with the SEC on November 3, 2026, disclosing beneficial ownership of 500,000 Units of Rainier Acquisition Corporation as of September 30, 2026.

Key Highlights

  • Reporting person: Sio Capital Management, LLC, a Delaware limited liability company and registered investment adviser, filed the disclosure.
  • Units held: Sio reported beneficial ownership of 500,000 Units, each consisting of one Class A ordinary share and one-quarter of one redeemable warrant to acquire one Class A ordinary share (CUSIP G73591110).
  • Percent of class: The 500,000 Units represent 5.67% of the class, based on 8,825,000 shares outstanding following the September 2, 2026, issuances.
  • Voting and dispositive power: Sio reported 0 shares with sole voting or sole dispositive power, and 500,000 shares with shared voting power and shared dispositive power.
  • Control structure: Both Sio and its general partner, Sio GP, LLC, are controlled by Michael Castor, who may be deemed to control voting and dispositive decisions over the reported shares.
  • Event date: The date of the event requiring the filing was September 30, 2026.

Sio Capital Management's Ownership Position in Rainier Acquisition Corporation

According to the Schedule 13G filed November 3, 2026, Sio Capital Management, LLC disclosed that as of September 30, 2026, it beneficially owned 500,000 Units of Rainier Acquisition Corporation, whose principal executive offices are located at 1 Penn Plaza, 48th Floor, New York, NY 10119. The filing states that the 500,000 Units represent 5.67% of the class, calculated based on 8,825,000 shares outstanding following the September 2, 2026, issuances, as derived from the issuer's Form 8-K filed September 3, 2026.

The filing describes Sio as "a registered investment adviser to certain affiliated funds that directly hold the shares of Common Stock to which this statement relates for the benefit of their respective investors," and states that in this capacity Sio has voting and dispositive power over such shares. All 500,000 Units are reported under shared voting power and shared dispositive power, with no sole voting or dispositive power claimed. Sio GP, LLC serves as the general partner to the relevant client funds, and both Sio and Sio GP, LLC are controlled by Michael Castor, according to the filing.

The filing includes a footnote stating that "neither the filing of this Schedule 13G nor any of its contents shall be deemed to constitute an admission by the GP or Michael Castor that such person is the beneficial owner of any of the equity securities referred to herein for purposes of Section 13(d) of the Exchange Act, or for any other purpose, and such beneficial ownership is expressly disclaimed." The statement was signed by Jin W. Lee, Chief Compliance Officer of Sio Capital Management, LLC, on November 3, 2026.

What Was Disclosed

Sio Capital Management, LLC filed a Schedule 13G disclosing beneficial ownership of 500,000 Units, equal to 5.67% of Rainier Acquisition Corporation's outstanding Units, as of September 30, 2026, with all power held on a shared basis through affiliated funds.