At the moment, we just cannot say for sure. Xbox/Microsoft has acquired Zenimax Media, the parent company of Bethesda Game Studios. However, according to Phil Spencer, there are no immediate plans to make Bethesda games exclusive to Xbox, and they have honored timed exclusive deals with Sony like the one present for Deathloop. However, we would say that this attitude will not last too long, and we would not be surprised if gaming fans will be forced to get an Xbox Series X/S to enjoy future Fallout titles.