Microsoft has hired OpenAI co-founders Sam Altman and Greg Brockman to head up a "new advanced AI research team," the software conglomerate's chief Satya Sam Altman and Greg Brockman and many of their former OpenAI colleagues will join Microsoft, Satya Nadella said.
Sam probably still controls a ton of shares, so I think effectively this would give them >50% of shares as long as they are partnering.