Microsoft announced on Monday that it has hired Sam Altman and another co-founder of ChatGPT maker OpenAI after they unexpectedly departed the company days earlier in a corporate shakeup that shocked the artificial intelligence world.

Microsoft Chairman and CEO Satya Nadella also tweeted that the major investor in OpenAI “behind the chatbot that kicked off the generative AI craze “looked forward to getting to know” OpenAI’s new chief executive, former Twitch leader Emmett Shear, and the rest of the management team.