It will operate as both a 200-400mm or a 280-560mm lens.
Canon has been known to announce the development of new lenses well before they hit the market and their latest tease comes in the form of a very interesting pro-super-telephoto lens. The EF 200-400mm f/4 IS USM extender looks a lot like the rest of Canon's beige pro lenses. But, it has an integrated 1.4x extender that can be turned on and off. That means it can be both a 200-400mm and 280-560mm lens in one body.