Jane Street, the powerhouse Wall Street trading firm, lost about $15 billion in July partly due the troubles at hedge fund Situational Awareness, according to people familiar with the matter.

It was the firm's worst monthly loss ever, one of the people said. Jane Street is still enjoying its best trading year with revenues of more than $40 billion through July, the person said, but the losses are surprising for a firm known for its risk management. Losses on AI stocks exacerbated the pain.

Situational Awareness is the hedge fund led by former OpenAI employee Leopold Aschenbrenner. He built a $45 billion investment firm at the center of the AI trade, making aggressive, borrowing-fueled bets along the way. Jane Street, which rarely allocates money to outside managers, became a major investor in the hedge fund.

Aschenbrenner's bets soured in July, sending his fund into a tailspin. Aschenbrenner sold the bulk of Situational's stock portfolio to Ken Griffin's investment firm Citadel after suffering deep losses.

A quant-trading firm that has piled up profits in recent years, Jane Street lost money in other ways last month, too, as quant traders suffer through a rough period. Trades in China were losers for a number of quants, and firms suffered as AI-related stocks tumbled then snapped back.

The Financial Times earlier reported on Jane Street's July loss.

Jane Street has long been known as a secretive firm and an unusually flat organization, with no one leader serving as its public face. But it has been edging into the spotlight more recently as it seeks to become an AI powerhouse.

Jane Street has surged in size from a handful of staffers when it was founded 26 years ago to 3,500 employees, and it wants to get much bigger, with plans to recruit more than 500 employees this year.

In April, Jane Street cut a deal to invest $1 billion in AI computing company CoreWeave and spend $6 billion to use its AI cloud platform.