Getting a 4k surface?

Using the Nvidia Shield TV on our 4K Tv the output is 4k according to the TV.

But when running our games (native gles2) on the device I cannot get a larger surface than full hd (1920x1080).

I’ve looked at this article

But when I look at the SurfaceHolder frame size when getting the surfaceCreated event it says 1920x1080.

So how do I enable a 4k output in my games?