During the Xbox Podcast, where Xbox put out their plans for the brand, they revealed that Activision-Blizzard games are coming to Game Pass, with the first being Diablo IV on March 28th. The news was confirmed by Xbox President Sarah Bond.

There is no word on when the other games, whatever they are, will arrive, but given Xbox rolled out the Bethesda games over months, I would expect the same to happen here.