The cable is cooled by a mix of water and glycol, which runs through the cable and also cools the connector pins. Tesla use this in their supercharger cables, as without it the cable would be too heavy.

https://www.cpcworldwide.com/Liquid-Cooling/Electric-Vehicle...

At 1000V, 1000A require 0.13cm wire diameter[0] over 2 Meter with 5V voltage drop, just 15 AWG.

[0] https://www.omnicalculator.com/physics/amp-to-wire-size