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.
Game Mode VRR could - in theory - see the complete elimination of screen-tear from console video gaming without the judder associated with traditional v-sync, and could also allow developers to target arbitrary frame-rates as performance targets as opposed to the standard 30fps or 60fps (though we wouldn't expect to see this occur too often as older screens will still be the main target). Although it is an HDMI 2.1 feature, the new 48G cable isn't required for today's resolutions - and in theory, this element of the protocol could be retrofitted to existing consoles paired with HDMI 2.1 screens (as we've seen in the past with PS3 3D and PS4 HDR support added to existing consoles via firmware updates). Of course, support in new screens will depend upon manufacturers fully supporting the HDMI 2.1 spec.
The HDMI forum press release has more details and there's a full spec here. First impressions? It seems to be a fully fleshed out 'next-gen' HDMI specification that looks forward many years into the future of display technology - and explicit game mode support offering an incredibly valuable feature can only be a good thing. The question is how much of the HDMI 2.1 spec will make its way into consumer-level 4K screens - and when.