iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2016-03-31T16:55:04Z. The update package is 1.14 GB. 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: 5f4c26cc1b4a0e97f239b75980310f6560c32f1d.zip.