Currently, the page isn't showing info, but just the name. AMD has not announced the Radeon RX 500X series just yet if and when it will be available is also unknown. An earlier rumor indicated respin product that would get a 5% boost in performance, that same rumor indicated a launch in June or July, likely Computex time.
Radeon RX 580 and 570 are already respin RX 480 and 470, all based on the AMD Polaris GPU. You can see URL placeholders for the RX 580X, RX 570X, RX 560X, and RX 550X on the AMD website.