Stability AI, the closely watched artificial intelligence startup, has lost at least two top executives in recent weeks, including its head of research and chief operating officer.

David Ha, head of research for the London-based startup, resigned this month. Chief Operating Officer Ren Ito also left in June. Ha declined to comment. Ito didn’t immediately respond to requests for comment.

In an emailed statement, Stability AI spokesman Motez Bishara wrote, “We can confirm that David Ha has taken a break from employment at Stability AI for personal reasons.” He also said, “Ren Ito has left to pursue other interests. We wish them both well and thank them for their contributions to Stability AI."

The departures follow an article in Forbes that said Stability AI’s founder and chief executive officer, Emad Mostaque, had a “history of exaggeration.” Mostaque denied the allegations in a lengthy blog post. At the Bloomberg Technology Summit on June 22, Mostaque responded to the report. “I have Asperger’s and ADHD, and I have a very definitive view of the future,” he said on stage. “I think that shocks people because they can’t deal with the exponentials.”

Last valued by investors at $1 billion, Stability AI is known for popularizing Stable Diffusion, an open-source image generator it released publicly in August 2022. The startup didn’t create the product, but Stability AI supported its development and has said that most of its original researchers now work for the company. Stable Diffusion emerged as a key rival to OpenAI’s Dall-E, and Stability AI has since trained and released numerous versions of the tool.

Before joining Stability AI, research chief Ha previously worked at Alphabet Inc.’s Google Brain division, where he was a research scientist focused on generative artificial intelligence, technology that can generate content such as text or images. Ha joined Stability AI in October, where he was involved in recruiting and led the company’s research efforts.

Ha and Ito are not the only high-profile people to leave the startup this year after a relatively short tenure. In an interview with Bloomberg in May, Christian Cantrell said he worked at Adobe for 20 years before he joined Stability AI as vice president of product in October. There, he was responsible for offerings such as Stability AI’s application programming interfaces and its DreamStudio software. DreamStudio can be used to produce and edit images via the Stable Diffusion image generator. Cantrell said he left at the end of March to start his own company.

--With assistance from Mark Bergen.