Netflix started streaming 4K content back in 2014 which began with House Of Cards. Now they are planning to add more HDR support for future content.
http://www.digitaltrends.com/home-theater/netflix-plans-for-hdr-dolby-vision-interview-neil-hunt/
See details at Digitaltrends
The first Netflix program to support HDR is Marco Polo: Marco Polo
More info on Dolby Vision @ dolby.com