The 4K based Xiaomi Mi Box III had previously focused on Chinese audiences interested in accessing a wide range of Chinese TV shows and movies many of which are free to watch (and not 4K). With the recently announced, 4K Mi Box (2016), Xiaomi is now going after the US market with support of Android TV 6.0, Google Cast, and a large stable of popular streaming media channels like Netflix which also support 4K content.
Unlike the Chromecast Ultra which supports the more mainstream HDR technologies, HDR10 and DolbyVision, Xiaomi decided not to support DolbyVision and instead opted for the royalty free HLG HDR technology introduced by BBC and NHK that is better optimized for the needs of TV broadcasters.
As of the time of this writing, Xiaomi was not yet taking orders on their website. We look forward to testing the 4K Mi Box (2016) when it becomes available.