iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 5s (Global), released on 2018-04-24T17:10:04Z. The update package is 761.17 MB. This is a delta (partial) update that requires 11.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 70d478cdcd2501136aa2e17f58ced4dbd7bda221.zip.