iOS 8.3 (build 12F70) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2015-04-08T17:56:14Z. The update package is 458.9 MB. This is a delta (partial) update that requires 8.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 90819d95b31da7a1b322def220ee58b66fce9f56.zip.