This number WILL include variants such as tanker and AWACS, due to PLA's lack of access to other large airframes. US air fleet, if you include tankers and AWACS, does exceed a thousand.
And this number is the life time of production -- so a late Y-20 may replace an early Y-20. So the active fleet may be smaller, but do consider at the end of production life of Y-20, Chinese economy will be multiple times the size of US economy -- that implies the ability to sustain and the possible need consistent with the larger scale.
How many years has Y-8/9 been in service with PLAAF and how many have they produced (including all the special missions variants)? Let's also include H-6 for the sake of the argument since Y-20 would also replace the tankers.
It would be not such a good thing if PLAAF is still producing Y-20s in 50 years.