iOS 12.1.2 (build 16C101) is an official Apple over-the-air update for the iPhone X (GSM), released on 2018-12-17T21:06:17Z. The update package is 1.54 GB. This is a delta (partial) update that requires 11.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 378b596d7a6e370cca669fe644bbc4336c01397f.zip.