iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 8 Plus (GSM), released on 2018-04-24T17:09:35Z. The update package is 807.02 MB. This is a delta (partial) update that requires 11.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8e201198aae6f49a5960f92773dff30fa1609c24.zip.