HDMI 2 was an incremental improvement over HDMI 1.4. It improved the speed of transmission to 18 Gbps.HDMI 2.1 is an exponential improvement over HDMI 2 in that its speed is 48 Gbps. This is a huge increase in bandwidth.HDMI 2.1 supports 4K at 120Hz to 144Hz, and it can support 5K and 8K.If HDMI 2.1 is important to you, pay attention to the TV specs and shop accordingly.