This is a pre-release version of iOS 8.4.1 for iPhone, iPad, and iPod touch. Devices updated to iOS 8.4.1 can not be restored to earlier versions of iOS.
At this point it's unclear what's new; however, it's possible that Apple may be looking to close exploits used by the TaiG jailbreak or fix issues with Apple Music.
Developers can download the update from the link below.
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