Thinking Machines co-founder resigned due to stress; she may now join OpenAI
Days after leaving Thinking Machines Lab due to health concerns and stress, AI researcher Lilian Weng is returning to OpenAI. An OpenAI spokesperson confirmed her hiring to ‘The Information’. Weng will reportedly work on the company’s research into recursive self-improvement, which uses AI models to help build better AI systems.
Weng announced her departure from Thinking Machines on Monday, noting that July 29 would be her last day at the startup. In a message shared internally and later posted on X, she wrote: “I don’t feel I can continue at the pace a startup demands.” “The constant level of stress and workload have pushed me beyond what my health can physically handle.”
Calling it “an extremely difficult decision,” Weng added: “I feel terrible about letting down the people at Thinky, but at the same time, I am constantly worried about my health.” “I have been sick longer than I have ever experienced in my life.”
Despite leaving the startup, Weng made it clear she was not abandoning the field of AI. “I still love working in AI and enjoy reading research papers to keep up with cutting-edge advances,” she wrote. Explaining her reasons for resigning, she noted that “a role with defined responsibilities in a more predictable environment—rather than as a co-founder—will better suit the next stage of my life.”
What will Lilian Weng's role be at OpenAI?
Weng previously worked at OpenAI between 2018 and late 2024. During her time there, she helped establish the company’s Applied AI Research team, later led the Safety Systems team, and contributed to the development of GPT-4 in areas such as pre-training data, safety, evaluations, and deployment.
According to a famous publication Weng will now rejoin to lead a high-level team focused on recursive self-improvement. The research aims to use AI systems to accelerate the way future AI models are designed, trained, and evaluated. An OpenAI source told a famous publication that Weng’s combination of research experience, technical expertise, and leadership skills makes her ideally suited for the role.
Another major departure from Thinking Machines Lab
Weng’s exit marks yet another departure of a senior figure from Thinking Machines Lab, the AI startup founded in February 2025 by Mira Murati, OpenAI’s former chief technology officer. She becomes the fourth of the company’s six original co-founders to leave the project. Previous reports indicated that nearly a third of the startup’s founding members had left just months after its launch.
Of the original founders, only Murati and chief scientist John Schulman remain at Thinking Machines. Barret Zoph and Luke Metz previously left for OpenAI, while Andrew Tulloch joined Meta. Another report noted that Zoph subsequently left OpenAI in June. Reportedly, Weng is also the third member of the startup’s original founding team to return to OpenAI this year.
For her part, Murati publicly expressed her support for Weng’s decision. Responding to Weng’s post on X, she wrote: “We’ll miss you; it’s been wonderful building Thinky together. I’m glad you’re prioritising your health. Thanks for everything.”