Awaiting the release Diablo Immortal GameSpot published an interview with Senior Game Designer Scott Burgess. During the conversation, he spoke about the duration of the main campaign.
According to Burgess, the game will offer approximately 20 hours of story at launch. Once every few months, the developers promise to release updates with new dungeons, zones, and content that expands the story.

Burgess also assured players that all content would be free. The game can be monetized using expanded battle passes and premium cosmetic items.
Diablo Immortal comes out on June 2 for iOS and Android. Open testing of the PC version will begin at the same time as launch, but the game will not be available to Russians.
Source: VG Times