Microsoft has confirmed that the Xbox One X supports HDMI 2.1 and will hopefuly be certified before launch. Currently, the new console is certified for HDMI 2.0 but according to Microsoft’s Mike Ybarra, the 2.1 certifications will hopefully be done in time for launch.
Certified for 2.0 now. Will certify for 2.1 when the spec is finalized (it isn't yet, hopefully by Nov).
— Mike Ybarra (@XboxQwik) August 29, 2017
While a minor update of 0.1 might not sound like much, the new certification does mean a lot. HDMI 2.0 for example has a capacity of 18 Gbit/s which is impressive, but HDMI 2.1 has a theoretical capacity of 48 Gbit/s. That extra bandwidth means that the connection can handle more data and higher resolutions of 7680 x 4320 (8K) at 60Hz, or if you prefer 3840 x 2160 (4K) at 120 Hz.
The Xbox One X launches on the 7th November 2017.