iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 8 (GSM), released on 2018-04-24T17:09:33Z. The update package is 744.71 MB. This is a delta (partial) update that requires 11.2.5 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 051d0216837101caa79369fce173575265370618.zip.