As of this week, you may notice that the Diablo III game launcher and Battle.net desktop app will begin downloading data for a "future patch." This download is in preparation for the March 25 launch of Reaper of Souls, as well as a pre-expansion patch that will be released in the coming months.
How it Works:
The download will be around 6GB in size and include things like models, textures, art files, and other upcoming content in patch 2.0.1 and Reaper of Souls that is already complete. By making this data available early, you'll have less to download once the pre-expansion patch and expansion are released.
The background download data is encrypted and won't make any changes to the live game or Battle.net service until patch 2.0.1 and Reaper of Souls launch. In the meantime, you will be able play Diablo III as normal, and your in-game experience should remain unaffected by the download itself.
In order for the background download to begin, Diablo III must be installed on your computer and patched up to the latest build. Please note that you will be eligible for the background download even if you have not prepurchased Reaper of Souls.
If you're using the Battle.net desktop app:
If you're using the Battle.net desktop app, the background download will continue as long as the application is running. The download can be paused at any time by clicking the Pause button located to the right of the circular background download icon. To resume the download, click the Resume button (which will appear in the same location as the Pause button) or click the Installation & Updates Options button and select Resume Updates.
The Battle.net desktop app also let's you customize your background download settings, so you can pause updates whenever a game is launched as well as set your preferred download speeds. To adjust your preferences, click the Installation & Updates Options button located to the left of the background download icon and select Settings.
If you're using the standard Diablo III launcher:
If you're using the standard Diablo III game launcher, the background download will continue to pick up data so long as the game launcher is running. You can always check the progress of your download by clicking the Info button at the top of the launcher, then selecting Connection Information from the drop-down menu. If you wish to complete the update at a later time, simply click the Play button at any point to pause the background download and run Diablo III, or simply close the launcher.