The future of OpenAI remained uncertain on Tuesday after extraordinary efforts by employees and investors to oust the board had so far failed to persuade its directors to resign and reinstate co-founder Sam Altman.

People with direct knowledge of the matter said that by the end of Monday, 747 out of 770 OpenAI employees had signed a letter threatening to quit and join Microsoft if the board refused to resign and reverse their decision on Friday to sack Altman.

Venture capitalists backing the generative artificial intelligence start-up were also exploring legal measures to force the board to reverse course, according to multiple people with knowledge of their thinking.