iOS 8.3 (build 12F70) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2015-04-08T17:56:15Z. The update package is 450.65 MB. This is a delta (partial) update that requires 8.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 81e12136901db3b546a19d88ccc9b3ebb85e73e6.zip.