UPDATE 29/9/16 8:40am: Digital Foundry has assessed World at War's performance on Xbox One, concluding that the game runs more smoothly than the same code operating on original Xbox 360 hardware. It's not the night and day improvement seen in Call of Duty 2, but many of the smaller sub-60fps dips in both campaign and zombie mode are ironed out.
Original Story: Call of Duty: World at War is now available to play on Xbox One via backward compatibility.
Call of Duty: World at War is coming to Xbox One Backward Compatibility today. Now, all back compat COD titles are purchasable on Xbox One pic.twitter.com/NsLkdJJGqu— Larry Hryb (@majornelson) September 27, 2016
2008 shooter World at War was developed by Treyarch, which went on to make the Black Ops series of Call of Duty games.
After the 2007 release of Modern Warfare, World at War returned to a World War 2 setting, and it added a co-op mode.
Crucially, World at War included a Nazi Zombies minigame, the precursor to the phenomenally popular Zombies mode now a part of every Call of Duty.
Other Xbox One backward compatibility additions include E4: Every Extend Extra Extreme, Encleverment Experiment and FunTown Mahjong.