iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 8 (GSM), released on 2017-12-13T18:11:02Z. The update package is 65.88 MB. This is a delta (partial) update that requires 11.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 705c5c443dea41e41eeebf3bb63a14da21056b1d.zip.