[Stefan Mileschin]

While the first HDMI 2.1 48G-branded cables were announced back in late 2018, they were not formally certified by the HDMI Forum for one reason: the certification program for HDMI 2.1 was not ready then and it is still not ready now. Yet, numerous developers of cables are already demonstrating prototypes of their HDMI 48G products that are marked as Ultra High Speed HDMI. Furthermore, makers of televisions are prepping the first Ultra-HD TVs that use HDMI 2.1.
UHS HDMI Certification Program

HDMI 2.1 48G cables use four data lanes operating at 12 Gbps each for an aggregate bandwidth of 48 Gbps, up from 18 Gbps today, yet retaining backwards compatibility with existing equipment. The additional bandwidth HDMI 2.1 offers enables it to support new Ultra-HD resolutions and refresh rates including, including 4Kp120, 8Kp100/120, 10Kp100/120, and upcoming color spaces, such as BT.2020 (Rec. 2020) with 10, 12, or even more advanced with 16 bits per color component. Actually, high resolutions and bit depths eat up 48 Gbps of bandwidth quickly, so for anything higher than 8Kp60 with 4:2:0 chroma sub sampling and 10-bit color, VESA’s DSC 1.2a link compression technology is used.

Since HDMI 2.1 48G cables as well as sources and sinks are physically different from existing HDMI 1.4/2.0 cables, makers of appropriate products have to adopt new manufacturing methods, whereas HDMI Forum has to introduce a new certification program that includes various compliance tests that ensure that interconnections work fine at high data rates and support all the features. Makers of cables are typically experienced enough to build HDMI 2.1 48G products, HDMI Forum admits. Since however there is no HDMI 2.1 48G certification program, they are not advised to sell products marked as Ultra High Speed HDMI Cables.

The HDMI Forum plans to make its UHS HDMI interconnection certification program available in the next several months, so expect ‘official’ HDMI 48G copper and optical cables to become available in the foreseeable future. Furthermore, once compliance tests are ready, makers of TVs will be able to mark their TVs as HDMI 2.1 compatible.

https://www.anandtech.com/show/14534...i-48g-incoming