The company that created ChatGPT was thrown into turmoil Monday after Microsoft hired its ousted CEO and many employees threatened to follow him in a conflict that centered in part on how to build artificial intelligence that's smarter than humans.

The developments followed a weekend of drama that shocked the AI field and fueled speculation about the future of OpenAI, which named a new chief executive on Friday and then replaced her on Sunday. The newest CEO vowed to investigate the firing of co-founder and CEO Sam Altman, who's been instrumental in OpenAI's transformation from a nonprofit research laboratory into a world-renowned commercial startup that inaugurated the era of generative artificial intelligence.

Microsoft, which has been a close partner of the company and invested billions of dollars in it, announced that Altman and OpenAI's former president, Greg Brockman, would lead its new advanced AI research team. Brockman, also an OpenAI co-founder, quit in protest after Altman was fired.

Hundreds of OpenAI employees, including other top executives, threatened to join them at Microsoft in an open letter addressed to OpenAI's four-member board that called for the board's resignation and Altman's return.

“If the architects and vision and brains behind these products have now left, the company will be a shell of what it once was,” said Sarah Kreps, director of Cornell University’s Tech Policy Institute. “All of that brain trust going to Microsoft will then mean that these impressive tools will be coming out of Microsoft. It will be hard to see OpenAI continue to thrive as a company.”

Microsoft CEO Satya Nadella wrote on X, formerly known as Twitter, that he was “extremely excited” to bring on the pair and looked “forward to getting to know” the new management team at OpenAI.

Altman later said on X that his top priority with Nadella is to ensure that OpenAI "continues to thrive” and that it is committed to “fully providing continuity of operations to our partners and customers.”

OpenAI said Friday that Altman was pushed out after a review found he was “not consistently candid in his communications” with the board of directors, which had lost confidence in his ability to lead the company.

In an X post Monday, OpenAI's new interim chief executive, Emmett Shear, said he would hire an independent investigator to look into Altman's ouster and write a report within 30 days.

“It’s clear that the process and communications around Sam’s removal" were handled "very badly,” wrote Shear, who co-founded Twitch, an Amazon-owned livestreaming service popular with video gamers.

He said he also plans in the next month to “reform the management and leadership team in light of recent departures." After that, Shear said, he would “drive changes in the organization,” including “significant governance changes if necessary.”

Originally started as a nonprofit, and still governed as one, OpenAI’s stated mission is to safely build AI that is “generally smarter than humans.” Debates have swirled around that goal and whether it conflicts with the company's increasing commercial success.

The reason behind the board's removal of Altman was not a “specific disagreement on safety,” nor does the board oppose commercialization of AI models, Shear said.

OpenAI last week declined to answer questions about Altman’s alleged lack of candor. The company's statement said his behavior was hindering the board’s ability to exercise its responsibilities.

A key driver of the shakeup, OpenAI’s co-founder, chief scientist and board member Ilya Sutskever, expressed regrets for his participation in the ouster.

"I never intended to harm OpenAI. I love everything we’ve built together and I will do everything I can to reunite the company,” he said Monday on X.

The open letter began circulating Monday. According to a copy obtained by The Associated Press, the number of signatures amounted to a majority of the company's 770 employees. The AP was not able to independently confirm that all of the signatures were from OpenAI employees.

“Everyone at @OpenAI is united,” one of the signatories, research scientist Noam Brown, said on X. “This is not a civil war. Unless Sam and Greg are brought back, there will be no OpenAI left to govern.”

The letter alleged that after Altman's firing, the company's remaining executive team had recommended that the board resign and be replaced with a “qualified board" that could stabilize the company. But the board resisted and said allowing OpenAI to be destroyed would be consistent with its mission, according to the letter.

OpenAI has said since its 2015 founding that its goal is to advance AI in a way that benefits all humanity.

A company spokesperson confirmed that the board received the letter.

Microsoft declined to comment on the letter.

After Altman was pushed out, he stirred speculation about coming back into the fold in a series of tweets. He posted a selfie with an OpenAI guest pass Sunday, saying this is “first and last time i ever wear one of these.”

Hours earlier, he tweeted, “i love the openai team so much,” which drew heart replies from Brockman and Mira Murati, OpenAI’s chief technology officer who was initially named as interim CEO.

It's not clear what transpired between the announcement of Murati's interim role Friday and Shear's hiring, though she was among several employees Monday who tweeted, “OpenAI is nothing without its people.” Altman replied to many with heart emojis.

The board consists of Sutskever, Quora CEO Adam D'Angelo, tech entrepreneur Tasha McCauley and Helen Toner of the Georgetown Center for Security and Emerging Technology. None of them responded to calls or emails seeking comment. Because of its nonprofit structure, the board differs from most startup boards that are typically led by investors.

Altman helped catapult ChatGPT to global fame based on its ability to respond to questions and produce human-like passages of text in a seemingly natural way.

In the past year, he has become Silicon Valley’s most in-demand voice on the promise and potential dangers of artificial intelligence.

Earlier this year, he went on a world tour to meet with government officials, drawing big crowds at public events as he discussed the risks of AI and attempts to regulate the emerging technology.

But as money poured into OpenAI this year, helping to advance its development of more capable AI, it also brought more conflict around whether that fast pace of commercialization fit with the startup's founding vision, said Kreps, the Cornell University professor. But rather than slow that pace, Altman's ouster may simply shift it out of OpenAI.

Altman "really has a walk-on-water aura, and I think a lot of it is well deserved," Kreps said. “He’s the one who has attracted the investment, and he’ll do that wherever it is.”

Microsoft's shares rose 2% on Monday and hit an all-time high. The AP and OpenAI have a licensing and technology agreement allowing OpenAI access to part of the AP’s text archives.