OpenAI named ex-Twitch boss Emmett Shear as interim CEO, while outgoing chief Sam Altman is set to join backer Microsoft (MSFT.O) in a surprise turn of events for the startup at the heart of an artificial intelligence boom.

The appointments, settled late into the night on Sunday, followed Altman’s abrupt departure just days earlier as CEO of the ChatGPT maker and ended speculation that he could return.

In a statement on the social media platform X, Shear dismissed speculation that OpenAI’s board ousted Altman because of a spat over the safety of powerful AI models. He vowed to open an investigation into the firing, consider new governance for OpenAI and continue its path of making technology like its viral chatbot available.

“I’m not crazy enough to take this job without board support for commercializing our awesome models,” Shear said, adding: “OpenAI’s stability and success are too important to allow turmoil to disrupt them like this.”

OpenAI dismissed Altman on Friday following a “breakdown of communications,” according to an internal memo seen by Reuters.

Altman was a founding co-chair of the startup that kicked off the generative AI craze a year ago by releasing ChatGPT, a chatbot that became one of the world’s fastest-growing software applications.

Microsoft Chief Executive Satya Nadella said in posts on X that Altman would become CEO of a new research group inside the software maker, along with other departing OpenAI colleagues such as outgoing President Greg Brockman who quit following Altman’s ouster.

Microsoft has invested billions of dollars in OpenAI and staked its future on the startup, releasing what it called AI copilots to business customers based on OpenAI’s technology.

Microsoft had supported a return of Altman to the startup, according to sources, a move that seemed likely only hours prior to Monday’s announcements. Teasing his expected reconciliation with OpenAI’s board, Altman had posted an image of himself on X on Sunday wearing an OpenAI guest badge with the caption: “first and last time i ever wear one of these.”

OpenAI researchers have viewed Microsoft’s vast reserves of computing power as essential to the development of super intelligent machines. Nadella and Shear both said their companies remained committed to their partnership, while resources would go to Altman’s new group at Microsoft as well.

“We look forward to moving quickly to provide them with the resources needed for their success,” Nadella said.

In a separate post on X, Altman shared Nadella’s message with the words, “The mission continues”.

The decision not to reinstate Altman as OpenAI’s chief confounded efforts by investors and employees to steady the startup’s path.

They feared his abrupt sacking could lead to a mass exodus of talent and impact an upcoming $86 billion share sale.

Shortly after the internal announcement of Shear’s appointment, distraught employees “streamed out” of OpenAI headquarters in San Francisco, The Information reported.

Dozens of staffers internally announced they were quitting the company on Sunday night, according to the report, citing a person with knowledge of the situation. Several leaders of the startup posted on X on Monday: “OpenAI is nothing without its people.”

Shear co-founded Twitch and had stepped down from the Amazon.com-owned live video streaming platform earlier this year.

Some of the recently departed researchers, such as Szymon Sidor, are joining the new effort at Microsoft, OpenAI’s now-former President Brockman said in a post on X.

Long in conflict has been OpenAI’s mission to build technology to benefit humanity, and that of its investors who have bankrolled the effort expecting a financial return, said analyst Richard Windsor of Radio Free Mobile.

“This weekend was simply the detonation of a bomb that has been waiting to go off,” he said.

Governing OpenAI is a non-profit. Its four-person board as of Friday consists of three independent directors holding no equity in OpenAI and its Chief Scientist Ilya Sutskever.

Reporting by Jeffry Dastin and Anna Tong in San Franciso, Urvi Dugar and Shubham Kalia in Bengaluru and Stephanie Kelly in New York Editing by Nivedita Bhattacharjee, Miyoung Kim, Sam Holmes and Susan Fenton