The game is available as a digital download for $14.99. Those who previously purchased Spartan Assault for Windows 8 or Windows Phone 8 before Dec. 15, however, can pick it up for $4.99.
Halo: Spartan Assault takes place between the events of Halo 3 and Halo 4. The game follows the rise of Commander Sarah Palmer and the beginning of the Spartan Ops program. In addition to online cooperative multiplayer, the game also features new enemies, weapons and achievements.
Halo: Spartan Assault is expected to launch in January 2014 for Xbox 360; the port was originally slated for release this month.