dpreview has add recently released Sony Alpha a9 (Amazon/B&H Photo/Adorama) in their studio comparison tools. Now we can play the high ISO images of Sony a9 compare to other related cameras. We compared Sony Alpha a9 and Nikon D5, Canon EOS-1D X Mark II. You can see the detail RAW images below:
Sony Alpha a9 Vs. Nikon D5 at ISO 102,400:
It clearly see that Nikon D5 is much better than Sony a9.
Sony Alpha a9 Vs. Canon EOS-1D X Mark II at ISO 102,400:
Both cameras are similar at ISO 102,400. Sony a9 is a bit better.