Ex‑OpenAI Researcher’s Fund Discloses 5% Stake in Nebius

A fund run by former OpenAI researcher Leopold Aschenbrenner disclosed roughly a 5% stake in Amsterdam‑based Nebius, and the company’s shares rose 11% to a two‑week high after the regulatory filing. The filing showed Situational Awareness holds 12.41 million Class A shares, a holding valued at about $2.6 billion as of Wednesday. Data compiled by LSEG put the stake at roughly 5% to 5.6% of Nebius’s shares outstanding.

Nebius shares have climbed more than 151% so far in 2026. The filing identifies Situational Awareness as the company’s largest shareholder following the disclosure.

Aschenbrenner previously worked on OpenAI’s Superalignment research team before leaving to focus on investments in companies tied to AI development and infrastructure. He named his investment firm after a 2024 essay that argued superhuman artificial intelligence could emerge as early as 2027. Situational Awareness managed about $13.67 billion as of March 31, a 148% increase from the end of 2025, and holds stakes in other AI infrastructure firms including CoreWeave and IREN.

Nebius has reported rapid revenue growth, with quarterly revenue increasing nearly eightfold year over year. The company announced a $643 million acquisition of Eigen AI in May and disclosed an AI infrastructure supply agreement with Meta in March as part of efforts to expand capacity.

Some analysts have cautioned on valuation. D.A. Davidson analyst Gil Luria maintained a neutral rating earlier this month, noting the stock’s elevated valuation could limit near‑term upside. The filing naming Situational Awareness as the largest shareholder has drawn attention to Nebius amid growing demand for specialized AI computing resources.