From the MS press release:
From a technical standpoint, this will manifest as world-class visuals in 4K at 60FPS, with possibility of up to 120FPS, including support for Variable Refresh Rate (VRR), and 8K capability. Powered by our custom-designed processor leveraging the latest Zen 2 and next generation RDNA architecture from our partners at AMD, Xbox Series X will deliver hardware accelerated ray tracing and a new level of performance never before seen in a console. Additionally, our patented Variable Rate Shading (VRS) technology will allow developers to get even more out of the Xbox Series X GPU and our next-generation SSD will virtually eliminate load times and bring players into their gaming worlds faster than ever before.