Apple seeds iOS 8.4 download links for all, who want update his iPhone, iPad and iPod Touch. If you have one of iOS 8.4 supported devices - you can download such ipsw. What the next? Jailbreak iOS 8.4.
Unfortunately, but jailbreak teams like TaiG or Pangu unconfirmed official new about jailbreak 8.4 release date. We think that second way for jailbreak will be only after iOS 9 release date, because iOS 8.4 has minor updates for devices.
iOS 8.4 works perfect on iPhone + Apple Watch. If you bought new Apple's Watch, you must update your iOS, because new iOS 8.4 aims for fix some bugs in iOS 8.3.
If you have jailbroken iPhone or iPad - stay on last jailbroken iOS.