Recent tweets and an interview hint at the existence of a sequel.
A tweet from Jean-Philippe Caro, creative director at Ubisoft, teased that the ZombiU team is working on a prototype for a ZombiU sequel.
Caro later tweeted that not all prototypes become games. However, our earlier interview with Florent Sacré, the creative and artistic director of ZombiU, and the Producer Guillaume Brunier, suggested the idea of ZombiU being a franchise. They said "We have a hard time squashing this theory. ZombiU is not a remake of Zombi. True it’s a tempting thing to believe as there are similarities but we only realized this afterwards. Now if that helps ZombiU being a franchise, we should stop fighting for the truth!" You can read that interview here.
