Bethesda categorically opposes retcons in Fallout series and will only expand existing canon

As the Fallout universe expands beyond video games, Bethesda lead writer Emil Pagliarulo confirmed that the studio is categorically against revising existing canon. He considers preserving the universe's integrity one of the greatest honors of his work.

In Fallout, [all of] the lore matters, and if you think it doesn't, the internet will remind you that it does. It's important to Fallout fans, whether something was made pre-war or post-war, it all matters. And it's a huge responsibility.

Pagliarulo has carried this responsibility for many years, working as a quest designer on Fallout 3 and lead writer on Fallout 4 and Fallout Shelter. In parallel, he participated in developing Skyrim and Starfield.

I actually consider that one of the biggest honours and responsibilities of my job, keeping the lore together and tight. Retconning is a terrible thing generally – you don't want to change something that's come before. We never want to retcon, but we do like to add on to the existing fiction, and do that in a way that doesn't spit in the eye of what came before, and that's a challenge a lot of times.

The Prime Video series hasn't introduced major changes to canon, though it recently established one of the endings from Fallout: New Vegas as official for the show. One of the showrunners, Geneva Robertson-Dworet, noted that the creators didn't intend to single out a specific ending as the only correct one.