> Looking closer at the Steam Machine's specs, one will see that the HDMI 2.0 port delivers up to 4K/120Hz and supports HDR, FreeSync, and CEC. Those are all HDMI 2.1 specs — which technically means the Steam PC is HDMI 2.1-compatible. The only reason the new hardware can't boast the official 2.1 classification is that the HDMI Forum will not allow HDMI 2.1 on Linux devices, the OS that powers all Steam hardware.

(emphasis mine)

Microsoft is a member of the HDMI Forum. In a just world, those two things together would be grounds for legal action.