Lilian Weng leaves Thinking Machines, rejoins OpenAI
Original: Thinking Machines co-founder Lilian Weng left the company citing health reasons, then joined OpenAI
Why This Matters
Weng's return to OpenAI to lead recursive self-improvement research highlights intensifying AI talent competition and signals OpenAI's strategic prioritization of self-improving AI systems.
Lilian Weng, co-founder of Thinking Machines and former OpenAI VP of AI Safety Research, announced her departure from the startup on July 27, 2026, citing health issues. OpenAI confirmed on July 29 that she would rejoin to lead a team focused on recursive self-improvement research.
Lilian Weng, a co-founder of AI startup Thinking Machines, announced her resignation via an internal Slack message shared publicly on X on July 27, 2026. She cited ongoing health concerns, writing: 'I don't feel I'm able to continue at the pace a startup requires,' and 'the amount of consistent stress and workload have pushed me beyond what my health can sustain physically.' She had previously served as VP of AI Safety Research at OpenAI before co-founding Thinking Machines alongside former OpenAI CTO Mira Murati. On July 29, OpenAI confirmed to TechCrunch that Weng would be rejoining the company. According to an OpenAI spokesperson, she will lead a top-level team dedicated to accelerating internal research, with a focus on recursive self-improvement — a process by which an AI system iterates on itself to become more capable. Murati publicly responded to Weng's post with support, writing: 'We'll miss you, it's been wonderful building Thinky together. I'm glad that you're putting your health first.' It is unclear whether Murati had prior knowledge of Weng's plans to return to OpenAI.