We've been talking about HDMI 2.1 for a long time now, but ever since January 2017 after it's announcement only a handful of TVs support it. Thing is, it does require a specifically optimized cable, certified even but that certification still is not finalized. That's about to change though.

The HDMI forum is bound to certify the first series of HDMI 2.1 compatible cables, and if you think that you could use any cable, well not really at high resolutions as these cables need to push 48 Gbps. Your ethernet jack for example very likely is 1 Gbps right? you see where I am going with this.

The cables will 4 data paths, with each path passing 12 GT/s. Minus error-correction and 16b/18b encoding overhead, you are left with 10.67 GB/s per path times four = ~42  Gbps in effective bandwidth. And that bandwidth is needed for 8K displays with 60 fps (with DSC) and 4K with 120 fps over a single cable.

Photos: AnandTech

HDMI Forum: Certification program for Ultra High Speed ​​HDMI 48G Nearly Done