When Fallout 76’s Wastelanders expansion launches on April 14, the entire game (including Wastelanders) will also be launching on Steam. Of course, many of our PC fans who have played the game through the Bethesda.net Launcher would also like to have the option to play on Steam, so we have a special offer just for you. From now through 11:59pm ET, April 12, if you have already purchased Fallout 76 on Bethesda.net, you have the opportunity to get the game on Steam, including Wastelanders.
All you have to do to get your free Steam copy of Fallout 76 is go here and link your Steam account to your Bethesda.net account before 11:59pm ET, April 12. When the Steam version is available, you will automatically receive your Fallout 76 entitlement.
Source: Official Fallout Website.