Aliens Versus Predator: Extinction is a real-time strategy game with a focus on unit management over base-building and resource gathering. Each species has a single resource that is used to summon or upgrade units, and methods of unit generation differ radically. Players must move through specific objectives in order to advance a level, ranging from killing certain enemies or performing tasks like repairing an object. Starting conditions are often dependent on story developments. Each species has a population cap that varies by level. The population cost of units varies drastically between species.[7]
Human units, appearing in the game as the US Colonial Marines, gain credits by killing enemies and repairing atmospheric processors.[7] These credits can be spent on upgrading existing units or calling in new ones via dropship, which drop units off at specific landing beacons. Marine units are entirely medium to long range fighters and have support units to perform specific actions that aren't available to humans like other species (such as healing).
Predator units can only gain resources by killing opponents, which is granted via an "honor" system.[7] As the units gain honor, more units can be summoned via drop pods. Predators can self-heal and cloak themselves, but deplete energy reserves when doing so. There is only one Predator support unit, which improves the rate of energy regeneration.
Alien units gain resources by either killing or immobilizing opponents, which can be used on upgrades to specific units.[7] Unlike humans and Predators, Aliens cannot summon specific units at will and must instead bring corresponding host species to their hive to infest them. All Aliens, with the exception of "pure-bred" strains, have specific hosts that generate them. In order to generate eggs that can infest host units, Aliens must maintain a queen unit at their hive. This queen continuously lays eggs until the population cap has been reached.
The single player campaign spans 21 missions, with 7 levels per species.[5]