It’s not free. You can buy a season pass ($80 approx) or a 7-day pass ($25) but I think most people who called it free were coming and going after the attendant leaves the gate for the evening. So it’s free to camp but cost to enter the recreational area.
*Note: if you’re a veteran you are allowed to enter all national parks free of charge.
We have not stayed there this year but there was no permit required last year. A Ranger came around periodically and logged in license plate #'s in his computer to tell if people were exceeding the 14 day limit.
The site is within a National Recreation Area, so you have to either pay an entrance fee or have a National Parks pass. The stay itself is free and you don't need any special permit to camp (at least not when we visited).