Here comes the first stress test for the Classic beta, and Blizzard will be inviting a lot more people this time around. It's taking place this Wednesday, May 22nd and will last for 2 hours from 4-6pm PDT, but the realm itself will be available for a full day. All races and classes will be available, but the max level will be set to 5. Also, current beta testers will not be able to play their beta, but will have to join the new stress realm and make new characters if they want to play.
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
WoW: Classic is scheduled for August 27 (technically August 26 if you're in the Americas). The soonest that you can play it is starting in May, during Blizzard's scheduled stress tests. To opt-in you must have an active subscription on your Battle.net account. If you do, go to Account Management and select the Wow Classic beta. Keep in mind, there will be level caps during the test. The schedule is as follows: