iOS 12.1 (build 16B92) is an official Apple over-the-air update for the iPhone 6s, released on 2018-10-30T17:16:59Z. The update package is 1.35 GB. This is a delta (partial) update that requires 11.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a54ee86585a646e84f232a14b7bd31f1140c4bca.zip.