I feel the best way is to use a calibrated CT ( current transformer ) which is readly available in Market ( selected shops ) .

Just one month back i was doing some measurement with 10000 Amps ( ten thousand Amps !!!! ) . I was using readymade CT which give 200mV @ 4000 Amps !!!!

Like that you can select 1000 Amps CT which will give you 200mV .

If you need the address of the shop where you can get the CT , I can provide you .

the problem with the Shunt method is that the voltage across the shunt when 900Amps is flowing is just 75mV ...and you won't get any isolation.

If you are using CT , you are isolated from the 900V line

So wish you all the best ...

Regards
LAL