From The Truth About Guns:

The CPX-4 comes complete with an optimized recoil system, the innovative Roebuck Quad-Lock Technology that promises repeatable accuracy, ambidextrous manual safety, and three 10-round magazines. The biggest improvement from their CPX-1 and CPX-2 (both 9mm) is the noticeably effortless slide by utilizing an optimized recoil spring assembly. Existing SCCY fans and new customers alike will take notice of the easy manipulation when racking their CPX-4 handgun.