“During the 2015 UCI professional road season, all teams will have the opportunity to use bikes with disc brakes at two events of their choice during August and September,” the governing body stated.
“The testing will continue in 2016 at all events on the UCI professional road calendar and, if the experience is satisfactory, disc brakes will be officially introduced to the UCI WorldTour in 2017. The aim is to eventually introduce disc brakes to all levels of road cycling.”
http://cyclingtips.com.au/2015/04/uci-confirms-disc-brakes-to-debut-in-peloton-this-august/