iOS 9.9.10.3.1 (build 14E304) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2017-04-03T17:00:27Z. The update package is 1.43 GB. This is a delta (partial) update that requires 8.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 43d9b3f74d0e0c1746c9c61f25aeb47a4643fee9.zip.