it's an AI startup they acquired earlier that's been doing this stuff
Discussion
yes sounds not very likely for openai to be strategically acquired by MS instead of google, surprising for what MS having done
Google already has good AI researchers working for them and have similar AI models, but Microsoft is much freer to act in this space. they have hardly any reputation in search so any crazy stunt they pull will be good PR for them. any crazy stunt Google pulls will be bad PR for Google.
no one takes Bing seriously so Microsoft has nothing to lose and everything to gain by disrupting the search space.
if you've been following what Microsoft has been doing in the software development space since Bill Gates left, you'll see that their approach has radically changed.