there is no aTV4 any more.
What was the aTV4 is now called the aTV-HD. (name change only, hardware is the same)
and then there is the aTV-4k
the aTV-HD will do 1080
those 2 services should stream in 1080,
one small note, some services are reducing their top qualities at the moment, to help with bandwidth on the main networks, since a lot of people are home streaming. I don't believe anyone is dropping below 1080 though,