iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-04-24T17:09:51Z. The update package is 1.3 GB. This is a delta (partial) update that requires 10.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 89b5f03b8547af1ac2bdae0486ce4e26b26ba9b0.zip.