Blizzard has confirmed it has "no plans" to launch Diablo 4 on Xbox Game Pass in the near future, as some might assume due to the Microsoft-Activision deal. Therefore, if you want to enjoy it on Xbox, you have to purchase a copy.
Rod Fergusson, who oversees Diablo's development at Blizzard, commented on the subject on Twitter (via VGC), revealing the studio has been getting a lot of questions about the potential launch of Diablo 4 on Game Pass. Unfortunately for some, there are currently "no plans" for that at the studio, meaning you'll have to own a copy of the game on your Xbox platform to explore this new dark version of Sanctuary from day one.
However, Fergusson's statement doesn't mean that Diablo 4 won't be available via the gaming subscription service at a later date. As of now, the $69 billion buyout of Activision Blizzard by Microsoft is still undergoing investigations by anti-competition authorities, and, if everything goes well, won't be fully closed by at least August-September 2023. With that in mind, there's a chance that Diablo 4 may join Xbox Game Pass optimistically by the end of the year, but this is merely speculation at this point. Most likely, an agreement to bring the game to the service hasn't been discussed by the two parties yet.
Diablo 4 launches on June 6, but we'll get to taste the game even sooner, as its early beta will run from March 17 to 19 for those who pre-ordered the title or got an access code via the KFC promotion.
Everyone else can join the open beta running from March 24 to 26. You can expect to complete the prologue and the entirety of Act 1, and will be able to reach level 25 with any of the starting characters.