Former OpenAI President and co-founder Brockman had quit over Altman's firing on Friday.
Meanwhile, tech publication Wired on Monday published what it said was a letter from some of OpenAI's most senior staff members threatening to quit en masse and follow Altman to Microsoft unless the company's board was replaced.
"Your actions have made it obvious that you are incapable of overseeing OpenAI," said the letter.
Signatories included the company's chief scientist, Ilya Sutskever, and even one member of the four-person board that had ousted Altman.
Microsoft is OpenAI's key business partner and has invested billions of dollars into the startup and helped provide the computing power to run its AI systems.
"We remain committed to our partnership with OpenAI," Microsoft's Nadella said as she announced Altman would join the company. "We look forward to getting to know Emmett Shear and OAI's new leadership team and working with them."
Former Twitch CEO brought in at OpenAI
OpenAI on Monday named Emmett Shear as an interim CEO to take over from Altman. Shear was previously the CEO of social media company Twitch.
The company caused further headlines over the weekend by initially announcing that Mira Murati would take over Altman's role, only to later demote her again and leave the top job open once more.
What does Altman's removal mean?
The tech world was shocked by Altman's sacking at OpenAI. He and the company shot to fame last year amid the hype surrounding the release of a new large language model, ChatGPT, and other products like the image-generating AI Dall-E.
Many emplyoees were also blindsided by the abrupt change in management.
Major investors had pushed for reinstating him. However, the board stood by its decision, saying it was "the only path to advance and defend the mission of OpenAI."
"Put simply, Sam's behavior and lack of transparency in his interactions with the board undermined the board's ability to effectively supervise the company in the manner it was mandated to do," the board said in the memo.
Investors had said Altman's sudden removal could lead to an exodus of talent from the company, and affect an upcoming $86 billion share sale.
tg, msh/wmr (AFP, Reuters)