According to details provided by the HDMI Forum, the new HDMI v2.1 specification will be backward compatible with all previous HDMI standards but will also need the new ultra high-speed HDMI cable for those new upgrades.
As for those upgrades, the HDMI v2.1 standard will offer 48Gbps of bandwidth, which is a significant improvement over 18Gbps of bandwidth on the HDMI 2.0. It will also bring higher resolution reaching 8K@60Hz without the Display Stream Compression (DSC) and 10K@120Hz with DSC. It also features the new Auto Low Latency Mode (ALLM).
Another big novelty for HDMI is support for Dynamic HDR as well as the Variable Refresh Rate (VRR) technology, which should reduce lag, frame stutter, skipping and freezing as well as deal with that pesky frame tearing. Unfortunately, HDMI Forum did not provide a lot of details regarding the VRR technology and we are not sure how different it is from AMD FreeSync.
In addition, the HDMI v2.1 standard will also include eARC, as well as Quick Media Switching (QMS), which eliminates the delay that can result in a blank screen before content is displayed and the Quick Frame Transport (QFT) feature which also aims to reduce latency in gaming and real-time interactive virtual reality content.
According to the press release, the HDMI v2.1 Compliance Test Specification (CTS) will be published in stages from Q1 to Q3 2018 and will notify the HDMI adopters as it becomes available.