Thinking Machines Co-Founder Lilian Weng Departs for Health Reasons, Then Joins OpenAI

Lilian Weng, co-founder of Thinking Machines, announced her departure from the startup this week, citing health issues due to the intense pace and stress of the role. In an internal Slack message shared on X, she stated she could no longer sustain the workload. Shortly after, OpenAI confirmed to TechCrunch that Weng will rejoin the company, where she previously served as VP of AI Safety Research. She will lead a top-level team focused on accelerating internal research, specifically on recursive self-improvement—a process enabling AI systems to iteratively enhance themselves. The move appears contradictory to her health concerns, though she may face less direct pressure as a non-founder. Thinking Machines co-founder Mira Murati publicly supported Weng's decision to prioritize health, though it is unclear if Murati knew of Weng's return to OpenAI. This high-profile departure highlights fierce talent competition among AI labs.