It appears that the P226 S4 is a regular 226 with a threaded barrel, raised sights and a plate to attach a lanyard at the base of the gun, all with the intent of using it with a suppressor. I have several 226's and they are great weapons, I personally don't like the raised sights as they are noticeably higher than any other platform. You could insert a threaded barrel into any 226 as another option. Sig has made the Threaded Barrel version of the 226 with raised sights before, this model adds the base plate for the lanyard.