Same as usual for an AP: slightly better than 10-top flamed (not quilt!) maple, choice of neck and FB woods, hybrid hardware, other color choices, and other nice treats.
EDIT:
For example, look at the CU22 product, page, and click on "Show Artist Package Specs" at the bottom.
Note that not all AP options are always available for every model - e.g. I think the HBs don't allow pickup swapping.
http://www.prsguitars.com/index.php/electrics/core/custom_22_2018
Top Wood Artist Grade Flame Maple
Back Wood Select Mahogany
Neck Wood Select Mahogany
Neck Profile Pattern
Optional Neck Wood Artist Grade Figured Maple or East Indian Rosewood
Fretboard Wood Artist Grade Gaboon Ebony
Fretboard Inlays Green Ripple Outline/Green Abalone Center Artist Bird Inlays
Headstock Gaboon Ebony Headstock Veneer with Inlaid Green Abalone Signature
Optional Artist Grade Fretboard & Veneer Figured Maple (Maple Neck Only) or Brazilian Rosewood (USA only)
Bridge PRS Patented Gen III Tremolo
Hardware Type Gold, Hybrid or Nickel
Pickups 57/08 Covered or Uncovered, 59/09 Uncovered, \ m / Uncovered, HFS & Vintage Bass, 58/15 or 85/15