The Xbox 360 devkits had extra USB ports for emulating DVD drives and high-speed data transfer. These kits required a fair amount of labor to put together; they

The Xbox 360 devkits had extra USB ports for emulating DVD drives and high-speed data transfer. These kits required a fair amount of labor to put together; they were $10,000, and often hard to obtain. I believe the Xbox One devkits are just production units with different key material (which prevents commercial titles from running, and allows developer-signed bits to run). Theoretically any Xbox One is a devkit, with the right software provisioning.