Bethesda today has stated that Fallout 4 will be getting a season pass. Although, the actual details of the season pass as a whole are still a mystery.
The pass will cost $30 (about £28) and will include all content to be released for Fallout 4. Whether this is all new storylines or (like Skyrim) an expansion for you settlement to build new homes etc, remains to be seen.
The first piece of DLC will be landing in the first quarter of 2016.