Some of the other improvements in the new version of HDMI include eARC support for object-based audio and advanced audio signal control, wider dynamic HDR, and "Game Mode VRR" allowing a GPU to change the refresh rate of the image on the fly.
Version 2.1 of the HDMI specification was developed by the HDMI Forum's Technical Working Group whose members represent some of the world's leading manufacturers of consumer electronics, personal computers, mobile devices, cables and components.
As with previous versions of the specification, HDMI 2.1 and the new cabling are backwards compatible to older equipment. The new specification will be available to all HDMI 2.0 Adopters and they will be notified when it is released early in the second quarter of 2017.
At present, the entire Apple product line supports some flavor of HDMI through either a direct HDMI connection, or an embedded HDMI implementation in Lightning, USB 3.0 or 3.1 type-C, or Thunderbolt 3. Apple only supports the older HDMI 2.0 specification that will be supplanted by the new version of the specification in the 2016 Retina MacBook, and the late-2016 Retina MacBook Pro across a USB-C to HDMI 2.0 adapter.
While the HDMI Group says that a firmware upgrade is possible to upgrade HDMI 2.0 devices to the new spec, whether or not that is possible "depends on manufacturer implementation."