Fallout 4 isn't out yet, not until November, but that hasn't stopped Bethesda from talking about its future.
As is the fashion nowadays, Fallout 4 will come with an optional Season Pass that for a one-off fee will get you automatic access to any DLC released for the game. For our North American friends, that'll cost $30. At the current exchange rate that's £20, which seems fair if we get a similar range of DLC for Fallout 4 as we did for Fallout 3.
That said, all we have is Bethesda's word that they "know that it will be worth at least $40" and a reminder that they could even do more than that. Of course, they've left out the part where they could also do less. They also have no information on what the DLC will entail, which I guess makes sense given that they're trying to avoid "spoiling" even the base game.
Stepping away from ways in which Bethesda wants more of your money, there'll also be regular free updates to the game, as with Skyrim. While bug fixes are essential in a Bethesda game, we can also apparently expect new features, maybe even ones based on feedback from players: "We'll work with all of you to figure out what new things you'd love to see added to Fallout 4," they say.
Also free is the Creation Kit, which will be released early next year. Once again, it's the same tool the team uses in the studio, and will let PC players create mods that can then be shared with others—even those playing on consoles.