4 wire resistance measurements with 2000 DMM?

I have one Keithley 2000 digital multimeter. I would like to do the 4 wire resistance measurement with the resistance in milli-ohm scale. I am wondering if Keithley 2000 provide constant voltage or constant current during 4-W resistance measurement. In either cases, what is the supplying voltage or current?

For milliohm measurements the Keithley 2000 would use 100-ohm range, with a 1mA source current.