Was at Quakecon and saw the Fallout 4 presentation.
it was awesome!
Todd Howard said Perks every level.
When you level up, you go to the Perk Chart on your Pipboy.
The chart was shown briefly hanging on the garage and is in your pipboy.
The header row lists each Special Stat.
There are 10 perks listed under each one listed as 1 through 10.
What ever your rating in a Special Stat determines which perks you can take.
Have 4 in all seven Special Stats then you can chose from the the first through 4th rows on each stat.
Most perks can be taken more than once.
If you stat is not high enough then the perk is greyed out.
There are no level requirements.
To take Sniper (a Perception Perk on the ninth row), you have to have a nine in Perception.
So you start with a nine In Perception, you can start the game with Sniper.
This makes sense if the Sole Survivor is a vet.
There are 70 base stats and most of them but not all have four ranks.
So the Science Perk has Science Rank 1 through Science Rank 4.
Tod Howard said with all the Perk ranks there were something like a 170 perks total.
He said they found limiting what perks you can take by your Special Stats makes the Sole Survivor very unique with vary different play styles.