Is this the heaviest UAV ever? Wiki gives a MTOW of 45k pounds or 20 tons but the underlying source could be making it up I have no idea.
We do not have any reliable numbers for GJ-11's MTOW.
But given that we know it uses a WS-13 derivative engine, it is unlikely to be heavier than some other similar UAVs out there that have flown before.
For example, the X-47B uses a non AB F100 engine in a broadly similar airframe (one which is larger than GJ-11 by what we've been able to measure of GJ-11 in the past), and is almost certainly heavier than GJ-11.
We know X-47B has a MTOW of slightly over 20 tons.
Given GJ-11s powerplant, is may be similar to Phantom Ray (which uses a similar thrust category non AB F404 engine in a similar planform), about 16 tons MTOW.
As for the largest flown UCAVs, it likely goes to the Russian S-70 maybe followed by X-47B.