Diablo 3: Reaper of Souls will go live in a matter of days. Blizzard is encouraging players to log in before the expansion pack's launch by boosting the experience point gains for the next few days.
"To celebrate—this weekend only—we're doubling down on the +50% Bonus XP that's already available in Diablo III, and boosting it all the way to +100% Bonus XP," Blizzard said on Battle.net. "This +100% Bonus XP period ends on Monday, March 24 at 12:01 a.m. Pacific Time. So, (if you need to) update your Diablo III game files here, log in this weekend, and rack up some last-minute Paragon Levels to aid you in your upcoming crusade against death itself."
In a different blog post, Blizzard outlined all the other steps you need to take before launch. You have to upgrade to the Battle.net desktop app, a launcher for all Blizzard games. The desktop app will then optimize your installation, a process that could take up to 60 minutes.
The biggest part of the pre-launch preparation, though, is downloading Patch 2.0.1. This massive patch paves the way for Reaper of Souls by adding or changing many features. Patch 2.0.1 revises the Paragon progression system so that players earn bonuses for all characters in their account. It also introduced a smarter loot system so that players will get fewer but more meaningful drops. This removes the need for the auction houses, which Blizzard shut down earlier in the week.
If you want to play Reaper of Souls the moment the expansion launches, Blizzard recommends that you log in beforehand to avoid possible server queues. You'll be notified within the game when the expansion is available. There's no need for you to download another patch or relaunch the game. However, in order to access Act V, you have to exit to the main menu and then select the new Act from the Quest Select Window.
The exact launch time for Reaper varies by region. Here's the full schedule released by Blizzard: