iOS 8.3 (build 12F70) is an official Apple over-the-air update for the iPhone 5 (GSM), released on 2015-04-08T17:56:10Z. The update package is 419.78 MB. This is a delta (partial) update that requires 8.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 40bca045577653194e98c50b9e7a0ef6e2cef4ac.zip.