Beta is planned to run for five to six weeks and will include the Xbox One version in some capacity. Only the first eight acts will be included in the testing, with the final two kept under wraps for the expansion launch. Grinding Gear said that it will be sending out silent waves of invites during the beta but that players can secure a beta key by either purchasing one of the upcoming supporter packs or from having spent several hundreds of dollars on the game already.
The team said that prior to the beta start, it would be wrapping up the current Legacy challenge league. The beta period will be marked by “so many events” in the game, although the specifics of these have yet to be revealed.
Source: Beta FAQ