Lilian Weng, co-founder of Thinking Machines, revealed this week that she is leaving her position due to health concerns. "I don’t feel I’m able to continue at the pace a startup requires," she wrote in an internal Slack message, which she also posted on X. "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."

According to a company representative, Weng will now lead a top-tier team focused on accelerating OpenAI’s internal research. This group will support cross-research efforts in recursive self-improvement—a process where an AI system iterates on itself to become more powerful. This move might seem at odds with Weng’s statements about the toll of a fast-paced startup on her health, but she likely won’t face the same direct pressure in a role where she isn’t a co-founder.

Still, in a competitive landscape for AI talent, this high-profile departure stands out. Thinking Machines co-founder and former OpenAI CTO Mira Murati responded to Weng’s X post earlier this week, expressing support for her decision to prioritize health. "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 remains unclear whether Murati knew that Weng would rejoin OpenAI.