iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 7 (GSM), released on 2018-04-24T17:11:36Z. The update package is 733.81 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: c4ca2a35b8d8ea2e6f4d92e94b1e931bb7fd1543.zip.