Assassin's Creed 4: Black Flag is going to be a transitional title, with one foot in the current generation and another foot in the next. The PlayStation 4 version, naturally, will be able to pull off a few tricks that the current-gen versions can, and Ubisoft has talked about what we can expect from it.
In a video on the PlayStation.Blog, creative director Jean Guesdon and associate producer Sylvain Trottier talk about the tweaks. Improved graphics are the most obvious, including more small details in the world. The two also talk about the seamless ground-to-naval gameplay, that will let you run around a city, set sail, attack other ships, and board them, all without a loading screen. They also make a brief reference to friends being present in single-player, though they didn't go into detail about what this may mean. It could simply be a reference to PS4's built-in social functions.