A:Answer The 55S425 is a member of our 4-Series while the 55R613 is a member of our Award winning 6-Series. Both series include a built in Roku operating system, 4K UHD, and HDR Support. The 6-Series builds on this and has additional features such as Dolby Vision, wide color gamut, HDR Dynamic Contrast, etc. Hope this helps! Thank you, TCL Customer Support
