Blizzard did not enclude any PvE Raids in the game when it launched but they are expected to appear in Vessel of Hatred.
Following the reveal of the expansion's Pre-orders, Blizzard also included a tease[1] of new PvP conent stating:
Lurking within the shadows lies your next great challenge, filled with powerful tribulations and promising rewards. First of its kind to Diablo, this dungeon will require eager warriors to team up and take down various perils together. More details on this game mode will be revealed soon.
With the addition of raid-like gameplay, Blizzard will also need to add a proper group-finding system which is not currently in the game but is likely to launch in the Vessel of Hatred.
What is a Raid?
A raid is a large-scale group activity where players joing forces to take on more challenging content. This could involve defeating powerful bosses and difficult dungeons.
Raids often require planning, strategy and teamwork to complete due to the higher difficulty level and more complex scenario.