Twitch Prime announced a partnership with Overwatch today that includes 10 free standard loot boxes and one golden loot box that includes a guaranteed legendary item.
The website requires a log in to an active Twitch Prime account that will give a code to be redeemed through Blizzard for the loot boxes. Once redeemed the loot boxes will be available within the client on either the PC or PS4 and Xbox One.
The golden loot box will be available immediately once the code is redeemed. Meanwhile the first five boxes will be available in August while the second five of the 10 loot boxes will be available in October.
These boxes will require that the Twitch Prime account remain active for the duration of the event in order to get all the boxes. However, should the Twitch Prime account expire, the loot you get from your boxes will remain with your Blizzard account.