The following is the official statement of the HDMI Forum inc.

HDMI 2.0 does not define new data lines and connectors, interfaces, so it can maintain perfect backward compatibility with HDMI 1.x, and existing Class 2 data lines can be used directly.
 The HDMI Forum inc. announced that the HDMI 2.0 standard specification has been developed and released, greatly enhancing support for 4K Ultra HD transmission and improving on multiple video and audio technologies.

HDMI 1.4 can already support 4K, but subject to bandwidth, up to 3840 × 2160 resolution and 30FPS frame rate, HDMI 2.0 will expand the bandwidth to 18Gbps, can support 3840 × 2160 resolution and 50FPS, 60FPS frame rate.

It also supports up to 32 channels in audio and up to 1536kHz sampling rate. Other major improvements: 

1. Simultaneous transmission of dual video streams to multiple users on the same screen 

2. Simultaneous transmission of multiple audio streams to up to four users 

3. Support 21:9 ultra widescreen display 

4. Video and audio stream dynamic synchronization
      

5.cec extension to better control consumer electronics devices with a single point of control

HDMI 2.0 does not define new data lines and connectors, interfaces, so it can maintain perfect backward compatibility with HDMI 1.x, and existing Class 2 data lines can be used directly. As for whether the current device can be upgraded to HDMI 2.0, there is no such trend at present, and it is necessary for the manufacturer to update the hardware and firmware. 

HDMI Forum inc. also pointed out that HDMI 2.0 will not replace HDMI 1.x, but based on the latter enhancement, any device to support HDMI 2.0 must first guarantee the basic support for HDMI 1.x. 

The HDMI 2.0 Compatibility Test Specification (cts) is expected to be released by the end of this year. 

In addition, it can be confirmed that AMD Hawaii graphics card will not support HDMI 2.0, and it will have to wait until 2015, NVIDIA has no news.