From the PlanetXbox360.com feature interview:
"Class3 and Class4 are the codenames for two open-world zombie survival games being developed by Undead Labs exclusively for the Xbox 360. Class3 will support 2 player co-op and drop the player in a world where the zombie apocalypse has destroyed the world they once knew. Class4 will be the subsequent game to be released, and will be a complete online gaming world where thousands of players will live in the same world and be forced to combat the zombie outbreak together. The great thing about Class3 and Class4 is that escape is not possible, so it is not about killing zombies as much as it is about living among them and trying to survive. We caught up with the wonderful Emily Diehl, one of the producers at Undead Labs, to discuss Class3 and Class 4 in more detail."