OpenAI¡¯s biggest investors are pressing the company to reinstate Sam Altman as chief executive officer after the board¡¯s stunning decision to fire him on Friday, according to people with knowledge of the matter.

Microsoft, the startup¡¯s biggest backer with a more than $10 billion stake, is working with investors including Thrive Capital and Tiger Global Management to bring back Altman, said the people, who asked to remain anonymous discussing private information.