Thinking Machines Co-founder Lilian Weng Steps Down for Health, Then Rejoins OpenAI

Lilian Weng, co-founder of Thinking Machines, announced her departure this week, citing health issues. In an internal Slack message shared on X, she stated she could not sustain the pace a startup requires due to consistent stress and workload. On Wednesday, OpenAI confirmed to TechCrunch that Weng would rejoin the company, where she previously served as VP of AI Safety Research. A spokesperson said Weng will lead a top-level team focused on accelerating internal research, supporting cross-research work on recursive self-improvement, a process enabling an AI system to iterate on itself. The move may seem contradictory to her health statements, but she likely faces less direct pressure as a non-founder. Thinking Machines co-founder Mira Murati expressed support for Weng's health decision but it's unclear if she knew about the OpenAI move.