Today, Apple has seeded the fourth beta of an upcoming iOS 9.3 update 13E5214d to developers for testing purposes, two weeks after seeding the third iOS 9.3 beta and more than two months after the public release of iOS 9.2, the last major update to iOS 9. iOS 9.3 has been in testing since January 11.

The fourth iOS 9.3 beta is available as an over-the-air update and through the iOS section of the Apple Developer Center.
Apple has fixed the 1970 bug in Beta 4 that would occur when changing the date manually to January 1st 1970. The 1970 Bug would brick your device and even a DFU restore would not solve the problem. Previously, there was only a jailbreak tweak which would help prevent this from occurring when somebody else uses your phone or you may even accidentally change the date yourself.
Apple have also updated the icon in the Control Center and the time bug that occured in iOS 9.3 Beta 3.
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