The HDMI forum has announced the full HDMI 2.1 specification at this year's CES, revealing support for 4K, 8K and even 10K video up to 120Hz. These new higher resolution modes will require the use a new 48G cable, backwards compatible with current HDMI devices. There's also support for 'dynamic HDR', which apparently "ensures every moment of a video is displayed at its ideal values for depth, detail, brightness contrast and wider colour gamuts - on a scene-by-scene or frame a frame-by-frame basis."
However, it's the reveal of a 'Game Mode VRR' specification that is of most interest to us. It's new HDMI functionality that closely mirrors the G-Sync and FreeSync technologies available for PC monitors, described as offering a "variable refresh rate, which enables a 3D graphics processor to display the image at the moment it is rendered for more fluid and better detailed gameplay, and for reducing lag, stutter and frame-tearing". The HDMI forum says that the technology will work for both PC and game consoles.