Despite the fact that Bethesda only recently announced Fallout 4 back in June, the game has been in the development stage for a long time. In fact, the setting for Fallout 4 was decided before Skyrim was launched!
During an interview at QuakeCon Bethesda’s Marketing VP, Pete Hines released that the studio had been discussing Fallout 4 as soon as Fallout 3 was released back in 2008. Hines said the decision to place Fallout 4 in Boston was made before Elder Scrolls V: Skyrim was released.
Pre-Skyrim… The ideas for Fallout 4 started right after Fallout 3 and have gotten worked on and percolated since 2008… We’re talking about it’s infancy, we’re talking about jotting some stuff down, we’re talking about “I want to do it in Massachusetts, and have it be about this, this, and this.”
However, he went on to say that Fallout 4’s development began seriously after the studio had supported Skyrim for several years.
The point at which it really kicked into development, whenever it was when we put up the post that said “Hey, we’re done with Skyrim and moving onto the next project.”
The post Hines was referring to was published in April 2013, when Bethesda announced that the plans for Skyrim DLC were done and that they were moving to a new game.
Fallout 4 launches on November 10th for Xbox One, PlayStation 4, and PC. During QuakeCon Bethesda also announced a bunch of new details about the new game, and even revealed the Fallout Anthology for PC which has the first five games (1, 2, Tactics, 3 & New Vegas) all together in a mini-nuke.