Pre-orders and previews begin April 10, launches April 24.
Apple Seeds First Betas of iOS 7.1, Apple TV Software to Developers
According to the release notes, iOS 7.1 fixes some network connection issues and some other bugs. There is also a new Yahoo logo, as well as new burst mode upload options and a toggle for a 'dark keyboard' in the Accessibility settings, according to 9to5Mac.
Late last week, Apple released iOS 7.0.4 to all users, fixing an issue with FaceTime calls.