Sam Altman has returned as CEO of OpenAI just five days after being fired by the company's board, capping one of the most dramatic episodes in recent tech history. The reversal came after nearly all of OpenAI's 700 employees threatened to quit and join Altman at Microsoft.

The crisis exposed deep tensions between OpenAI's original nonprofit mission and its commercial ambitions. The board that fired Altman cited concerns about his candor and the pace of commercialization, but buckled under pressure from employees, investors, and partners.

A new board has been constituted with more traditional corporate governance experience.