Multiplayer features
Clans
Diablo 4 will support clans, with features like custom banners and a clan bank to store Gold and items.
Party
The max party size in Diablo 4 will be capped at 4 players. Players will follow the party leader's storyline.
Voice chat
Players will have a separate in-game voice chat channel for their clan and party, allowing for easy conversing.
Multiplayer settings
Couch co-op
Blizzard has created special UI screens to allow two players to play on the same console at once.
Cross-platform
In a first for the Diablo series, a player on a PC can play with another player on an Xbox or PlayStation.
Regionless play
The game is regionless, meaning a player in Asia can play with someone in Europe. It's also cross-platform.
Community
Discord servers
See the most popular Diablo-related Discord servers and a list of their Diablo 4 specific channels.
More fun with friends
Blizzard wants both solo and party play to be equally as fun, but admitted that, if they had to choose one, the game is more fun with friends. To foster more party play, Diablo 4 will contain new multiplayer features, like a party finding tool, voice chat channels for clanmates and party members, and clan banks and custom banners. Also, console and PC players can play together (i.e., cross-play support).