Shares of Nebius Group (NBIS) climbed sharply on Thursday after a fund run by former OpenAI employee Leopold Aschenbrenner disclosed a sizable stake in the AI infrastructure company.
The disclosure added fresh momentum to one of the year’s strongest-performing “neocloud” stocks.
Nebius shares rose 11% during trading, reaching their highest level in roughly two weeks.
Nebius shares have surged more than 151% in 2026.
The rally followed a filing showing that Aschenbrenner’s investment firm, Situational Awareness, owns 12.41 million Class A shares in Amsterdam-based Nebius.
According to Reuters calculations, the stake was worth approximately $2.6 billion as of Wednesday.
Based on data compiled by LSEG, the holding represents roughly a 5% to 5.6% stake in Nebius, making Situational Awareness the company’s largest shareholder.
AI investor backing boosts Nebius momentum
The disclosure marks a significant endorsement for Nebius as investors continue searching for companies positioned to benefit from rising demand for AI infrastructure and cloud computing capacity.
Nebius has increasingly attracted attention as part of the growing “neocloud” sector, which focuses on providing computing resources and infrastructure needed for artificial intelligence workloads.
Leopold Aschenbrenner previously worked as a researcher at OpenAI as part of the company’s “Superalignment” team, which focused on ensuring artificial intelligence systems remained aligned with human values.
The team has since been disbanded.
After leaving OpenAI, Aschenbrenner shifted toward investing in companies tied to AI development and infrastructure.
He named his investment firm Situational Awareness after a lengthy essay published in June 2024 that argued effectively that superhuman artificial intelligence could emerge as soon as 2027.
Situational Awareness managed approximately $13.67 billion as of March 31, representing a growth of 148% from the end of 2025.
In addition to Nebius, the fund also holds significant stakes in AI infrastructure companies CoreWeave and IREN.
Revenue growth and acquisitions fuel investor interest
Nebius has rapidly expanded during the broader AI infrastructure boom, supported by strong revenue growth and strategic acquisitions.
Earlier this month, the company reported that quarterly revenue increased nearly eightfold compared with the prior year period.
The company has also pursued expansion through acquisitions and infrastructure partnerships aimed at strengthening its AI capabilities.
In May, Nebius announced a $643 million acquisition of Eigen AI. Earlier in March, the company disclosed an AI infrastructure supply agreement with Meta.
Those developments have helped position Nebius as one of the emerging players benefiting from surging demand for AI computing resources from enterprises, developers, and hyperscale technology companies.
Valuation concerns remain despite AI optimism
Despite strong investor enthusiasm, some analysts remain cautious about the stock’s near-term upside after its massive rally this year.
D.A. Davidson analyst Gil Luria maintained a “neutral” rating on Nebius earlier this month, warning that shares could face limited upside in the near term given the company’s elevated valuation.
Still, growing demand for AI infrastructure continues supporting broader interest in the sector, particularly as investors search for the next wave of AI winners beyond the largest technology companies.
Nebius remains one of the most closely watched names within the rapidly expanding AI infrastructure market as demand for computing power continues to accelerate globally.
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