Lilian Weng, co-founder of AI startup Thinking Machines, announced this week that she is stepping down from her role at the company, citing health concerns — and will rejoin OpenAI, where she previously served as VP of AI Safety Research.
Weng shared her departure in an internal Slack message, which she also posted publicly on X on July 27, 2026. “I don’t feel I’m able to continue at the pace a startup requires,” she wrote. “After thinking about it for several months, I ultimately have to admit that the amount of consistent stress and workload have pushed me beyond what my health can sustain physically.”
On Wednesday, July 29, OpenAI confirmed to TechCrunch that Weng would be rejoining the company. According to a company spokesperson, she will lead a top-level team focused on accelerating OpenAI’s internal research, with a particular emphasis on cross-research work related to recursive self-improvement — a process that would allow an AI system to iterate on itself to become more powerful.
Thinking Machines co-founder and former OpenAI CTO Mira Murati responded to Weng’s post on X, expressing support for the decision. “We’ll miss you, it’s been wonderful building Thinky together. I’m glad that you’re putting your health first. Thank you for everything,” Murati wrote. It is unclear whether Murati was aware that Weng would be returning to OpenAI.
The move could appear at odds with Weng’s stated reasons for leaving — returning to one of the AI industry’s most active organizations after citing unsustainable stress — though as a non-founding employee, she may face a different level of direct pressure than she did at Thinking Machines. The departure is notable at a time of fierce competition for talent among AI labs, as the source describes it.
Source: TechCrunch