It has been confirmed by game designer Angela Del Priore at Blizzcon 2019 that Diablo IV will be an online-only game. This comes as a surprise for the community, but keep in mind that you’re still able to play alone on dungeons or missions. If you’ve played Diablo 3 on PC, then this isn’t really breaking news as the last Diablo installment required an internet connection to run, whenever you play multiplayer or single player.
Now, to be honest, this is a common requirement for every Blizzard game such as StarCraft, Overwatch, World of Warcraft, and Overwatch.
Even if Diablo 4 takes a lot from Diablo 2, this is one of the new features that the game will take from Diablo 3. The game will run on PC, PS4 and Xbox One, and there will be no exception when talking about the internet connection required. Diablo 4 was announced at Blizzcon 2019 and at the moment doesn’t have a release date.