Co-operative play will not be introduced to State of Decay via a title update, Undead Labs has told fans.

"There's been a flood of good news about State of Decay lately, and it's been both exhilarating and humbling to share it with you," wrote executive producer Jeff Strain on the game's forums. "It's always easy to share good news; but it's much harder to share disappointing news, and unfortunately that is what I must do today.

"Over the past few weeks we've been working with Microsoft to lay plans for the future of State of Decay, including future Title Updates, DLC, and possible sequels. As part of that process we've also been thoroughly evaluating the possibility of adding co-op multiplayer to State of Decay. While there are great things in store for State of Decay, unfortunately multiplayer is not one of them."

He added: "It's no secret the game has done well, so we now have the opportunity to realize some of our hopes - and your hopes - for how we reinvest in the game and make it even better. We know co-op is the most requested addition to State of Decay, and we've also continued to hope it might be a possibility after release. Unfortunately, after re-evaluating it over the past few weeks, we believe our original estimate of six months was optimistic; the actual time is probably closer to nine months.

"We could 'check the box' and shoehorn multiplayer in sooner than that, but it wouldn't be a great experience, and certainly not one we'd be proud of. It's not simply a matter of adding the technology, but also redesigning core game systems to support multiple players, and then adding new content designed for people to play together. It's easy to imagine how all that would come together - as many have said, the game is practically begging for it - but retrofitting the game to add that experience would take the rest of this year, and well into the next. Worse, it would preclude our ability to offer any other kind of support for the game, including Title Updates and DLC."

Strain says that it's simply not "feasible to retrofit" multiplayer into the game, but assured fans that the future of the franchise will be built around multiplayer.

"I can say definitively that multiplayer will be the absolute heart of any future State of Decay games," wrote Strain. "As many of you know, we've always had ambitious plans for the future of State of Decay, and those plans have not changed."

He concluded: "From the entire team at Undead Labs, I want to express our gratitude and appreciation to each of you for being here on the forums and giving us your thoughts, hopes, and opinions on the game every day. I'm not just talking to those of you who give us support and encouragement - although you give us the rocket fuel we need to keep going every day - but also those of you who provide constructive criticism and help 'keep it real'.

"Stay tuned for announcements on what we are going to do with State of Decay. We're just getting started."

Last we heard, State of Decay had sold over half a million copies and is sure to have sold more since.

A PC version is also on the way.