After having a new Sony TV for a few days, I had been noticing a difference in the crispness of 4k YouTube videos and videos on Netflix that I had previously looked up and knew to be in 4k.
Turns out you need to have the 12-dollar streaming plan to access 4k streaming video now. When you have that plan enabled, UHD 4K content will be labeled as such.
I'd imagine this applies to the Shield as well.
This isn't a device related thing, its a streaming related thing. 4k means more pressure on their servers. Regardless of the device you want to stream on, if you want 4K, you have to pay for the 4K plan.