Thinking Machines co-founder Lilian Weng steps down over health — and rejoins OpenAI to lead self-improving AI work
Lilian Weng, who spent nearly seven years building OpenAI's safety systems before co-founding Thinking Machines Lab with Mira Murati in February 2025, left the startup on July 29, writing that sustained stress and workload had pushed her past what her health could bear. Days later, OpenAI confirmed she is returning to lead a team on recursive self-improvement — AI that iterates on itself to get more capable — an area OpenAI's June governance blueprint called potentially the most consequential frontier safety issue of the coming decade. Of Thinking Machines' six co-founders, only Murati and chief scientist John Schulman remain.
Why it mattersThe researcher who wrote much of OpenAI's safety playbook now leads its work on AI that improves itself — a signal of how seriously that frontier is being taken. It also deepens questions about Thinking Machines, which has now lost four of six founders.
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