iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone X (GSM), released on 2018-04-24T17:09:41Z. The update package is 675.93 MB. This is a delta (partial) update that requires 11.2.6 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3ef25ff1e40d8d1d3e09b7d441f6c77b29fe30d2.zip.