The open beta weekend begins at 3:00 p.m. EDT today and lasts until 1:00 p.m. on Monday, April 23rd. During the beta, all five classes will be available, but players will be limited to a level 13 cap as they give the game a whirl.
To access the Diablo III open beta, you'll need a valid Battle.net account and a BattleTag. Despite playing in the open beta, participants won't be able to post in the beta forums and won't receive Beta Bucks to spend.
Asian players in Korea, Taiwan, Hong Kong, and Macau will be part of not this stress test but rather a separate invitation-only closed beta test starting on April 23rd.