Last week, the board fired Altman after "losing confidence in him."
Early this morning Microsoft CEO Satya Nadella made the announcement that Altman would be coming on board at Microsoft and would be forming a team at the Volehill.
Nadella also said Greg Brockman, the former president of OpenAI who quit in protest after Altman's sudden departure, would be joining the new AI division at Microsoft alongside Altman.
"We look forward to moving quickly to provide them with the resources needed for their success," Nadella said.
In a letter on Friday, OpenAI's board accused him of not being "consistently candid in his communications with the board, hindering its ability to exercise its responsibilities".
This left those who invested in the company, such as Microsoft, wondering who these dumb arses on the board were. Vole invested $10 billion in the company on the assumption that it would grow, rather than shrink.
OpenAI's board of directors consists of Ilya Sutskever and three independent directors - Quora chief executive Adam D'Angelo, technology entrepreneur Tasha McCauley, and Helen Turner from the Georgetown Centre for Security and Emerging Technology. They are expect to be removed from Microsoft's Christmas card list.
Over the weekend, employees and investors, including Microsoft, were pushing for Altman to be reinstated.
Reports this weekend suggested his sacking had angered current and former employees who were worried it might affect an upcoming $86 billion share sale.
But board director Ilya Sutskever told employees on Sunday night that Altman would not return, prompting many to announce they were quitting.
This leaves Emmett Shear, who is expected to be named the new interim chief executive, to stop the rot while there is still a company.
Shear is an internet entrepreneur who was previously chief executive at Twitch. His name has come up, although OpenAI said on Friday that its chief technology officer, Mira Murati, had been appointed interim chief executive. At the time of writing, it is unclear why Murati did not want to take up the poisoned chalice.
Altman has been the face of the firm's rise. More than that, he is seen by many as the face of AI.
He testified before a US Congressional hearing to discuss the opportunities and risks created by the new technology. He appeared at the world's first AI Safety Summit in the UK at the beginning of November.
His ousting sparked an outpouring of support from Silicon Valley bosses, including former Google chief executive Eric Schmidt, who called Altman "a hero of mine" and said he had "changed our collective world forever".