Apple released the fourth beta of iPhone OS 4 to developers late on Tuesday. The company didn’t detail what the latest beta build included, but early reports claim the updated version runs noticeably faster and added new wallpaper options.

Apple first showed off iPhone OS 4 in early April including features such as third-party app multi-tasking, the ability to organize apps in groups, a unified in box for email, Bluetooth keyboard support, and more.

iPhone OS 4.0 will be available this summer for the iPhone and iPod touch, and this fall for the iPad. The beta of iPhone OS 4 and the SDK for developing iPhone OS 4-compatible apps is available for developers now at the Apple Developer Web site.