His estate has been putting out a lot of stuff from his so-called 'vault' recently . . . and the people working with them on it told "Variety" that it'll be a full-length album of previously unreleased material. There's no title, but it'll be out September 28th.
There aren't many details, other than it will be more "time-specific" rather than a compilation of stuff from throughout his career. They're still sorting through all the stuff Prince had locked away, and it doesn't sound like this will be the last release.