The board of directors of OpenAI, the high-profile artificial intelligence startup, said in a note to employees on Sunday night that its former director, Sam Altman, would not return to his job, while also naming his second interim replacement in two days.

Hours later, in another surprising move, Microsoft said it was hiring Altman and Greg Brockman, president of OpenAI and the company’s co-founder, who resigned in solidarity with Altman. The two men will run an advanced research lab at Microsoft.

At OpenAI, Emmett Shear, former CEO of Twitch, will replace Mira Murati as interim director, the board said. Ms. Murati, a long-time OpenAI executive, had been appointed to that position after The expulsion of Mr. Altman on Friday. The board said Shear has a “unique combination of skills, experience and relationships that will propel OpenAI forward,” according to the memo seen by The New York Times.

At Microsoft, Satya Nadella, the tech giant’s CEO, said Altman would be CEO of the new research lab, “setting a new pace for innovation,” in an apparent contrast to the OpenAI board’s desire to be cautious. in AI development. technology. Mr. Nadella noted in a post to X, formerly known as Twitter, that Altman’s new group will operate as an independent entity within Microsoft.

Nadella left room for other unnamed colleagues who could join the two Microsoft co-founders. “We hope to act quickly to provide them with the resources necessary for their success,” she said.

Altman responded cryptically: writing in X, “the mission continues.” By Monday morning, more than 550 of OpenAI’s 700 employees had signed a letter saying they could resign to join Altman’s new project at Microsoft unless the startup’s board of directors resigned, three people who read the letter said. .

A Microsoft spokesperson declined to comment beyond Nadella’s posts on X. The letter was previously reported by Wired.

Altman’s firing surprised the tech industry and OpenAI investors, which include Microsoft, Sequoia Capital and Thrive Capital. Microsoft, which has invested more than $13 billion in OpenAI, only found out about Altman’s departure a minute before it was announced, while other investors discovered that he had been forced out via social media. They received no further information or updates over the weekend.

“The board strongly defends its decision as the only path forward and upholds OpenAI’s mission,” Sunday’s memo said, referring to Altman’s dismissal from the company on Friday. It was signed by each of the four directors of the company’s board of directors; Adam D’Angelo, Helen Toner, Ilya Sutskever and Tasha McCauley.

“Simply put, Sam’s behavior and lack of transparency in his interactions with the board of directors undermined the board’s ability to effectively oversee the company in the manner in which it was directed to do,” the memo said.

The departure of Altman, 38, also drew attention to a gap in the AI ​​community between people who believe AI is the most important new technology since web browsers and others who fear that moving too quickly to develop it could Be dangerous. Sutskever, in particular, worried that Altman was too focused on building OpenAI’s business without paying enough attention to the dangers of AI.

The board’s decision to remove Mr. Altman came as a shock to industry allies and rank-and-file employees who supported the charismatic founder. Silicon Valley investors and tech executives expressed their support for Altman and Brockman. On Friday night, Altman was pitching a new artificial intelligence company to investors and planned to start the company with Brockman.

Since OpenAI launched its successful chatbot ChatGPT almost a year ago, artificial intelligence has captured the public’s imagination, with hopes that it can be used for important work such as drug research or to help teach children. But some AI scientists and political leaders worry about its risks, such as the disappearance of automated jobs or autonomous warfare that goes beyond human control.

OpenAI has been the gravitational center of that discussion along with its former CEO, who has done more than anyone over the past year to make artificial intelligence a mainstream topic.

The board did not cite specific incidents involving Mr. Altman as cause for removing him. Rather, it stated that Mr. Altman had “lost the trust of the board” and that removing him was “necessary to preserve the board’s ability to execute his responsibilities and advance the mission of this organization.”

“It is paramount that any CEO be honest and transparent with his or her board of directors,” the memo said.

OpenAI and Altman did not immediately respond to requests for comment.

The AI ​​company has an unusual governance structure. It is controlled by a nonprofit’s board of directors who can decide the company’s leadership, and its investors have no formal way to influence decisions.

Some OpenAI employees pledged to leave OpenAI or join Altman’s potential new company if the board did not relent. But even as Altman made his pitch for a new company, investors were pressing for Altman and Brockman to return.

Throughout the weekend, Altman and his supporters pressured OpenAI’s board of directors with appeals from venture capitalists, other tech executives and employees. Microsoft led the initiative, three people said, and smaller investors channeled their concerns through Microsoft.

The effort, the people said, was aimed at showing the company’s board of directors how popular Altman was among OpenAI employees and throughout Silicon Valley.

The lack of details about the reasons behind Altman’s overthrow emboldened his supporters. Some argued that OpenAI’s nonprofit board could no longer support the business that OpenAI had become: one with 700 employees, numerous customers and corporate partnerships that is on track to post $1 billion in annual revenue.

Altman, Brockman and Sutskever created OpenAI in 2015 along with nine other people, including Elon Musk, the CEO of Tesla. The group founded the AI ​​lab as a nonprofit and said that, unlike Google and other tech giants, it would not be driven by commercial incentives.

In 2018, after Musk split from OpenAI, Altman transformed the lab into a for-profit company controlled by the nonprofit and its board of directors. Over the next few years, he raised the billions of dollars the company would need to develop technologies like ChatGPT.

Before joining OpenAI, Shear led Twitch through its transformation from a new platform called to a giant acquired by Amazon in 2014. He stayed on after the tech giant took over and only left earlier this year. , saying she was having a son.

Shear, a veteran video gamer, was seen as a competent leader on Twitch, but he had his critics. He was perceived to be too focused on cutting costs and turning the money-losing site into a more profitable business.

“We apologize for the abruptness of the process we felt was required by the situation,” the board said in its memo. “Even understanding the questions you have raised, we continue to believe our actions were necessary.”

On Monday, when OpenAI employees signed the letter saying they might leave to join Altman’s new project at Microsoft, one name stood out: Sustkever. He sent a message to X saying he deeply regretted his role in the board’s decision.

“I never intended to harm OpenAI,” he said. “I love everything we’ve built together and will do everything I can to bring the company together.”

Kellen Browning, Karen Weiss, Erin Griffith and Tripp Mickle contributed reports.