Leopold Aschenbrenner, the AI researcher whose hedge fund virtually collapsed over the summer, is getting active again in the financial markets via options.

His firm, Situational Awareness, has been buying options positions in stocks including Advanced Micro Devices, Bloom Energy and Coreweave, sources told CNBC's David Faber.

The moves were made late last week and early this week, the sources said. Other stocks where he was active include SK Hynix and SanDisk. Additionally, Situational Awareness bought options in the Roundhill Memory ETF (DRAM).

His reentry to the public markets comes after the hedge fund's assets fell to about $10 billion following a peak above $45 billion to start July. A rapid decline that month in AI-related stocks that Aschenbrenner was buying using leverage forced him to unwind his public equity positions to Ken Griffin's Citadel in a fire sale to stave off a collapse. The hedge fund held onto stakes in private companies like Anthropic.

It was unclear if Aschenbrenner was taking in any new money to fund the new activity, or if it was using assets left over in the fund after the July rout and Citadel sale.