A:Answer RYRY - The Q90T is 4K and has 8 million pixels on the screen no matter what size the screen, and the Q900TS is 8K, which has 33 million pixels no matter what size the screen. The bigger the screen, the more pixels, and one of the reasons why 8K is recommended. The Q900TS does 8K upscaling that includes Machine and Deep Learning - Texture Creation. Noise Reduction, Edge Restoration, and Fine-Detail Restoration. The Q90T has 4K upscaling - which is good -but does not include the Deep Learning that offers Fine-Detail Restoration. The 65Q90T has Direct Full Array 16X, Quantum HDR 16X, and a Quantum Processor 4K. The 65Q900TS has Direct Full Array 32X, Quantum HDR 24X, and Quantum Processor 8K. The Q900TS also has an Infinity Screen - near invisible bezel - it's beautiful! They both offer Smart TV Powered by Tizen, Universal Guide, Ambient Mode+, Multiple Voice Assistants, TV Plus, Mobile View, Samsung OneRemote, and are SmartThings Compatible. Hope this explains the differences for you! ^Cris