Bethesda.net, for the unaware, is Bethesda's controversial PC games store/launcher hybrid. When Fallout 76 first released, it was exclusive to this platform, which angered many of the company's long-time Steam customers. Frankly, the game's exclusivity might have been for the best where gamers are concerned. Fallout 76 launched in a pretty shoddy state, and you could argue that Steam faithfuls dodged a bullet by holding out.
When Fallout 76 comes to Steam on April 14, new customers will be getting a much better overall experience than those who bought the game on launch day. Fallout 76 has seen several content drops since release, and it'll receive another one the same day it arrives on Steam: the "Wastelanders" update. This update will add human NPCs and other highly-requested features to the game.
Returning to the focus of this article, we should note that there's a slight catch with Bethesda's new offer. If you don't redeem your Steam copy of Fallout 76 before April 12, you'll lose your chance to get it at all (for free, anyway). As such, we recommend taking advantage of the deal sooner rather than later.
Bethesda has full redemption instructions here, but in short, you just need to link your Steam account to your Bethesda.net account and the copy should be automatically be added to the former.
In other related news, Bethesda is handing out free copies of the Fallout Classic Collection to new Fallout 76 Steam players. Whether you get the game using the method mentioned above, or buy it for full price, you're eligible for the free Classic bundle. It includes Steam versions of Fallout 1, 2, and Tactics, and it'll be available between April 14 and April 28.