Lilian Weng leaves Thinking Machines to rejoin OpenAI amid health struggles

Prominent artificial intelligence researcher Lilian Weng has stepped down as co-founder of Thinking Machines Lab, citing serious health concerns after months of intense startup pressure. Shortly after announcing her departure, reports confirmed that Weng is returning to OpenAI, where she will lead a research team focused on recursive self-improvement—an emerging area of AI that aims to develop systems capable of improving their own training and performance. Her decision highlights the growing conversation around the personal cost of leading high-pressure AI startups, where relentless innovation often comes at the expense of physical and mental well-being.

In an honest message shared publicly, Weng revealed that the demands of building a rapidly growing AI company had taken a severe toll on her health. She explained that over the past seven months she had experienced more frequent and serious illnesses than ever before, yet felt guilty about taking time off while the company raced to launch its first open-weight AI model, Inkling. Weng acknowledged that, unlike software, human endurance has limits, and recognized that continuing at the same pace was no longer sustainable. Her decision reflects a broader challenge faced by many startup founders who struggle to balance ambitious goals with personal health.

Founded in 2025 by former OpenAI CTO Mira Murati and other leading AI researchers, Thinking Machines Lab quickly became one of the industry's most closely watched startups, raising $2 billion at a $12 billion valuation. Despite its rapid success, the company has experienced significant leadership turnover, with several founding members returning to OpenAI. Weng’s return places her back at one of the world’s leading AI organizations, where she previously built OpenAI’s safety team and led applied AI research.

In her new role, she will focus on developing AI systems capable of refining and improving themselves, an area that could shape the next generation of artificial intelligence. Her journey serves as a reminder that while AI technology continues advancing at an extraordinary pace, sustainable innovation also requires protecting the people driving those breakthroughs.