The main thing is the addition of the Panoramic Commander's Sight, which is not there currently on the Arjun.
This would be the tank commanders sighting system, while the gunner would have his own.
This sight gives the commander flexibility to search targets 360 degree, while the gunner engages the already identified target.
This would give the Arjun the Hunter-Killer capability.
Al Khalid has this system, and some other newer generation tanks also have this system.
Tank commanders can zoom 360 degree independently of the gunners sight, previously the tank commander and gunner used the same sight for target acquisition and engaging.
Check out AK picture and see 2 imaging systems on both its sides.
here see AK, on one side you will see the round housing for the Panoramic Commander Sight, while on the other side the rectangular housing for the gunners sight.