iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone X (Global), released on 2018-03-29T17:11:27Z. The update package is 676.04 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: af8c70b9cfe032f9d30d5a1994c1562a1c6fbc0d.zip.