...did you miss the video that franklin posted?
Now, one might state "but that video could have been taken last year when and only released now!"
...but then I'd point out the grey nose of the Y-20 and how the first Y-20 prototype had a very distinctive and ugly white nose while in yellow primer.
However one could also argue the video might have been taken inbetween painting the first Y-20 prototype, that maybe XAC had decided to paint the nose first, leave it outside, before painting the rest of it to the now standard black.
...then I'd rebut that actually, the first Y-20 prototype's nose remained white even when the rest of the fuselage was first painted black.
So therefore, yes it is virtually confirmed that is a second prototype.
Unless XAC decided to build a giant full size mock up and leave it outside for fun.