OpenAI co-founder Ilya Sutzkever said Tuesday he was leaving Microsoft-launch supported.

“I’m excited for what’s next – a project that’s very personally meaningful to me, about which I’ll share details in due course,” Sutskever wrote in X post in Tuesday.

The departure comes months after OpenAI went through a leadership crisis involving co-founder and CEO Sam Altman.

In November, OpenAI’s board said in a statement that Altman had not been “consistently candid in his communications with the board.” The question quickly began to seem more complicated. The Wall Street Journal and other media outlets reported that Sutskever was focused on making sure that artificial intelligence would not harm humans, while others, including Altman, were instead more eager to move forward with the delivery of new technology.

Almost all OpenAI employees signed an open letter saying they would leave in response to the board’s action. Days later, Altman returned to the company, and board members Helen Toner, Tasha McCauley and Sutkever, who had voted to remove Altman, dropped out. Adam D’Angelo, who had also voted to oust Altman, remained on the board.

When Altman was asked about Sutskever’s condition of a scaling speaking to reporters at the time, he said he had no updates to share. “I love Ilya … I hope we work together for the rest of my career, my career, whatever it is,” Altman said. “Nothing to announce today.”

On Tuesday, Altman shared his thoughts on Sutzkever’s departure.

“It is very sad for me; Ilya is one of the greatest minds of our generation, a guiding light in our field, and a dear friend,” Altman wrote. of X. “His brilliance and vision are well known; his warmth and compassion are less well-known, but no less important.” Altman said research director Jakub Paczocki, who has been with OpenAI since 2017, will replace Sutskever as chief scientist.

OpenAI announced new board members, including former ones Salesforce co-CEO Brett Taylor and former Treasury Secretary Larry Summers. Microsoft was given a non-voting observer position on the board.

In March, OpenAI announced its new board and the conclusion of an internal investigation by US law firm WilmerHale into the events that led to Altman’s ouster. Altman rejoined the OpenAI board, and three new board members were announced: Dr. Sue Desmond-Hellman, former executive director of the Bill & Melinda Gates Foundation; Nicole Seligman, former executive vice president and global general counsel of Sony and president of Sony Entertainment; and Fiji Simo, CEO and Chairman of Instacart.

The three new members will “work closely with current board members Adam D’Angelo, Larry Summers and Brett Taylor, as well as Greg, Sam and senior management at OpenAI,” according to a company announcement in March, citing OpenAI co-founder Greg Brockman.

The news of Sutskever’s departure comes a day after OpenAI released a new AI model and desktop version of ChatGPT, along with an updated user interface, the company’s latest effort to expand the use of its popular chatbot.

The update makes the GPT-4 model available to everyone, including free OpenAI users, chief technology officer Mira Murati said Monday in a live event. She added that the new GPT-4o model is “much faster” with improved text, video and audio capabilities.

OpenAI said it plans to eventually allow users to video chat with ChatGPT. “This is the first time we’ve really taken a huge step forward when it comes to ease of use,” Muratti said.

In 2015, Altman and Tesla CEO Elon Musk, another co-founder of OpenAI, wanted Sutskever, then a researcher at Googleto become the fledgling startup’s top scientist, according to the lawsuit Musk filed against OpenAI in March.

“Dr. Sutkever considered whether to leave Google and join the project, but ultimately a call from Mr. Musk on the day that OpenAI, Inc. was publicly announced, convinced Dr. Sutkever to commit to joining the project as Chief Scientist of OpenAI, Inc.,” the legal filing said.