Fallout 4 will benefit from extensive compression it seems, with the install currently being listed at under 30GB.
The Xbox Store page for the game states that the install will take up 28.12GB. It's unclear how much HDD space PS4 owners will need to clear, but the figure will likely be similar.
This may change between now and November 10th but hopefully not substantially, though as with any major game these days there will probably be an extensive day one patch to go along with it.