The update comes with a bunch of improvements to the existing Music app, as Gurman notes, which include a new design, a feature that lets you stream music via AirPlay directly from the Now Playing screen, a revamped Mini Player, and Recently Added songs and albums at the top of your library among other additions.
A "beta" release refers to an early version of a software that's not intended for public launch just yet. Beta testers try out this early version and report bugs and things that need to be fixed back to Apple.
In February, Gurman also reported that this is the update that could include Apple's streaming music service based on Beats Music. The beta version of the update that's just been made available, however, doesn't mention anything about this new music service based on Gurman's latest report.
That's not surprising - if Apple is indeed planning to launch a brand new music service, it likely wouldn't quietly roll it out in a beta release before its ready to make a formal announcement. But it still could find its way into the final release.
We're expecting to hear more about Apple's music service in June at its Worldwide Developer Conference.
The beta release for iOS 8.4 comes just days after Apple launched iOS 8.3, which brought hundreds of new emojis to the iPhone's keyboard.