Former OpenAI exec Mira Murati’s startup, Thinking Machines Lab, is saying goodbye to two of its co-founders, both of whom are headed back to OpenAI. Another former OpenAI staffer who went to work for Murati’s startup is also headed back to the company.

On social media on Wednesday, Murati announced the departure of Barret Zoph, the company’s co-founder and CTO. “We have parted ways with Barret,” Murati said in a post on X. “Soumith Chintala will be the new CTO of Thinking Machines. He is a brilliant and seasoned leader who has made important contributions to the AI field for over a decade, and he’s been a major contributor to our team. We could not be more excited to have him take on this new responsibility.”

Murati’s announcement made no mention of co-founder Luke Metz or other departures.

Just 58 minutes after Murati’s announcement of Zoph’s departure, Fidji Simo, OpenAI’s CEO of applications, announced that Zoph would be headed back to OpenAI. “Excited to welcome Barret Zoph, Luke Metz, and Sam Schoenholz back to OpenAI! This has been in the works for several weeks, and we’re thrilled to have them join the team,” Simo wrote on X.

Metz, who is a co-founder of Thinking Machines, previously worked for OpenAI for a number of years on the company’s technical staff. So did Schoenholz, whose LinkedIn profile still lists him as working for Thinking Machines.

Zoph previously worked for OpenAI as VP of research, and before that, worked for six years at Google as a research scientist. Murati, who served as the CTO of OpenAI until September 2024, left the company and co-founded Thinking Machines with Zoph and Metz. The startup, where Murati serves as CEO, has amassed significant financial support since then, closing a $2 billion seed round last July, with participation from Andreessen Horowitz, which led the round, as well as Accel, Nvidia, AMD, and Jane Street, among others. The round valued the company at $12 billion.

TechCrunch has reached out to both Thinking Machines and OpenAI for comment.

While talent moves between AI giants are common in Silicon Valley, the departure of co-founders from a startup less than a year after its founding is particularly notable. The loss of two co-founders simultaneously — especially when one served as CTO — could be perceived as a particularly meaningful setback for Thinking Machines, which had assembled a high-profile team of former OpenAI, Meta, and Mistral AI researchers.

The company has also lost other key personnel, including co-founder Andrew Tulloch, who left to join Meta in October. OpenAI itself has seen numerous co-founders depart to launch or join competing ventures, including John Schulman, who left for Anthropic in August 2024 before joining Thinking Machines Lab as Chief Scientist as its launch in February of last year.