The only survivors are the Xbetters. Are they humans? Are they machines? They are androids that developed through the most advanced AIs for the evolution of human civilization. Their metallic bodies have allowed them to survive the inclemencies of a brutal climate.
There is only one generation of Xbetters. Finite. They cannot reproduce. They can only survive. To do so, they must fight to keep themselves functioning. Every time they suffer damage they are repaired with parts from other androids that have fallen in battle. This is how each Xbetter is unique. Pure or a mash-up of parts, its history and temperament is unrepeatable.