Major game mechanics, enemy spawns, and character data are handled on Blizzard's servers. This means even for solo play, the local game client cannot function without communicating with the server. Installation Requirements:
Blizzard representatives have confirmed that they do not plan to support an offline mode. Server-Side Logic: diablo iv offline mode install
: Eliminates "rubber-banding" and lag-induced deaths (critical for Hardcore players). Major game mechanics, enemy spawns, and character data
Short answer:
The game world features other players in hubs and during world events (like World Bosses), which is integrated into the core engine architecture. Major game mechanics
While you cannot play without an internet connection, there are a few options that mimic an "offline" or solo feel: Why does Diablo 4 require internet connection?