According to details spotted by Techpowerup.com, the RX 560 XT is just a rebrand of an RX 570 and should fit between the standard RX 560 and the RX 570, packing 1,792 Stream Processors, 112 TMUs, and 32 ROPs. It has 4GB of 6.6Gbps memory on a 256-bit memory interface.
It is not clear if the RX 560 XT is based on Polaris 20 or Polaris 30 GPU.
Update: AMD has officially confirmed that the Radeon RX 560 XT is actually based on Polaris 10 GPU and comes as a response to the Chinese market demand, confirming it will most likely stay exclusive to China.
As the marketing material suggests, this is a China-only SKU and it is highly unlikely that we will see it available worldwide but it is nice to see the XT branding, even on a China-exclusive SKU.