Direct link here
"We have an idea of where the end is, what the end is. But of course Yves [Guillemot, Ubisoft's overall boss] announced we are a yearly title, we ship one game a year. So depending on the setting, depending on what fans want, we've given ourselves room to fit more in this arc. But there is an end." - Assassin's Creed 4 game director Ashraf Ismail