Former OpenAI exec Mira Murati’s startup, Thinking Machines Lab, has said goodbye to two of its co-founders, both of whom are returning to OpenAI. Another former OpenAI staffer who worked for Murati’s startup has also returned to the company.

On social media on Wednesday, Murati announced the departure of Barret Zoph, the company’s co-founder and CTO. “Barret and I split up,” Murati said in an X post. “Soumith Chintala will be the new CTO of Thinking Machines. He is a skilled and experienced leader who has made significant contributions to the field of AI for over a decade, and he has been a major contributor to our team.

Murati’s announcement did not mention co-founder Luke Metz or other departures.

Just 58 minutes after Murati announced Zoph’s departure, Fidji Simo, the CEO of OpenAI applications, announced that Zoph would be returning to OpenAI. “Excited to welcome Barret Zoph, Luke Metz, and Sam Schoenholz back to OpenAI! It’s been a few weeks, and we’re thrilled to have them join the team,” Simo wrote in X.

Metz, who a co-founder of Thinking Machines, then Working with OpenAI for many years on the company’s technical staff. So is Schoenholz, whose LinkedIn profile he is still listed as working at Thinking Machines.

Zoph previously worked at OpenAI as VP of research, and before that, worked for six years at Google as a research scientist. Murati, who serves as OpenAI’s CTO until September 2024, left the company and co-founded Thinking Machines with Zoph and Metz. The startup, of which Murati serves as CEO, has gotten a lot of significant financial backing since then, ending a $2 billion seed round in 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 Thinking Machines and OpenAI for comment. Wired reported that the split between Zoph and Thinking Labs not good. In fact, it is telling that Murati did not write more about him in his public message about his departure from the company.

While the movement of talent between AI giants is common in Silicon Valley, the departure of co-founders from a startup less than a year after its founding is extremely rare. The loss of two co-founders at the same time – especially when one served as CTO – can be considered a very significant setback for Thinking Machines, which assembled a high-profile group of former researchers of OpenAI, Meta, and Mistral AI.

The company also lost other key staff, including co-founder Andrew Tulloch, who left to join Meta in October. OpenAI itself has seen several co-founders leave to launch or join competitions, including John Schulman, who left Anthropic in August 2024 before joining Thinking Machines Lab as Chief Scientist as it launched in February last year.