Starting this Friday, all players with a valid Battle.net account can log in and help stress test the game and servers. Users can download the Diablo III client immediately, team up with friends, play each of the five heroic classes to level 13, and fight to save the world from the impending demonic invasion.
The Diablo III open beta weekend starts from Friday, 20 Apr at 12.01pm PDT till Monday, 23 Apr at 10am PDT. The game's official release is on 15 May 2012.
Source: Blizzard Entertainment