A:Answer The 50S525 is a member of our new 5-Series while the 50S425 is a member of our 4-Series. Both series include a built in Roku operating system, 4K UHD, and HDR Support. The 5-Series builds on this and has additional features such as Dolby Vision, wide color gamut, HDR Dynamic Contrast, an edge-to-edge glass display, etc. You can also visit www.tclusa.com/products/home-theater/5-series and scroll down to "Compare All Models" to see all models compared. Hope this helps! Thank you, TCL Customer Support