Thinking Machines co-founder Lilian Weng returns to OpenAI

Lilian Weng, a co-founder of Thinking Machines Lab, has left the company citing health reasons and subsequently joined OpenAI. Weng previously served as OpenAI's VP of AI Safety Research before co-founding Thinking Machines.

Why it matters: Weng's return is a notable reversal for a high-profile safety researcher who left OpenAI to help build a competitor alongside Mira Murati, and a reminder of how thin and fluid the senior safety-research talent pool remains across labs. Her departure also raises questions about Thinking Machines' leadership bench as it competes for talent against better-funded rivals.