Thinking Machines cofounder quit over stress, she may now join OpenAI

Just days after quitting Thinking Machines over stress and health concerns, AI researcher Lilian Weng is reportedly heading back to OpenAI. With her new role, she is expected to work on one of the company's most ambitious AI research projects.AI researcher Lilian Weng is reportedly returning to OpenAIDays after stepping down from Thinking Machines Lab over stress and health concerns, AI researcher Lilian Weng is reportedly returning to OpenAI. An OpenAI spokesperson confirmed her move to The Information. Weng will reportedly work on the company's recursive self-improvement research, which uses AI models to help build better AI systems.Weng announced her departure from Thinking Machines on Monday, saying July 29 would be her final day at the startup. In a message shared internally and later posted on X, she wrote, "I don't feel I'm able to continue at the pace a startup requires." “The amount of consistent stress and workload have pushed me beyond what my health can sustain physically."Calling it "an extremely hard decision," Weng further wrote: "I hate myself to let down people at Thinky but at the same time I'm constantly worried about my health." "I've been in sickness more than what I have ever experienced in my life."Despite leaving the startup, Weng made it clear she was not walking away from AI. "I still love working in AI and enjoy reading papers to learn about frontier progress," she wrote. Explaining why she was stepping down, she wrote "a scoped role in a more predictable place, and not as a cofounder, will suit the next stage of my life better." What will be Lilian Weng’s role at OpenAI?Weng has previously worked at OpenAI between 2018 and late 2024. During her time there, she helped build the company's Applied AI Research team, later led its Safety Systems team, and contributed to GPT-4 across pre-training data, safety, evaluations and deployment.According to the Financial Times, Weng will now rejoin and lead a senior team focused on recursive self-improvement. The research aims to use AI systems to accelerate how future AI models are designed, trained and evaluated. An OpenAI told FT that Weng's mix of research experience, technical expertise and leadership makes her well suited to the role.Another big exit from Thinking Machines Lab Weng's departure also marks another senior exit from Thinking Machines Lab, the AI startup founded in February 2025 by former OpenAI chief technology officer Mira Murati. She is now the fourth of the company's six original cofounders to leave. Earlier reports suggested that nearly a third of the startup's founding members had exited within months of its launch.Among the original founders, only Murati and chief scientist John Schulman are still with Thinking Machines. Barret Zoph and Luke Metz both left for OpenAI earlier, while Andrew Tulloch joined Meta. A separate report said Zoph later left OpenAI in June. According to reports, Weng is also the third member of the startup's original founding team to return to OpenAI this year.Meanwhile, Murati publicly supported Weng's decision. Replying to Weng's post on X, she wrote: "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."- EndsPublished By: Divya BhatiPublished On: Jul 30, 2026 10:55 IST