My experience with the Android app is that you can't trust that "Currently playing at" information. For example, look at the following:
In all three cases, this is what it was actually doing:
Amazon's app seems to be handling the upsampling itself, and to their credit, they're at least doing this with floating point, which avoids some of the most egregious errors that are audible at low volume with 16-bit integer-based interpolation, which is what Android's mixer will usually do:
However, Amazon's Android app is still re-sampling almost everything. As a result of this silly oversight, its SQ is not as good as Tidal's or Qobuz's, even for redbook FLAC, and you are not getting Ultra HD from any Android device right now (even on Android devices that are perfectly capable of playing back 44/16, 96/24, 192/24, etc.). Amazon's Ultra HD claims in the Google Play Store are false advertising.