iOS 12.1 (build 16B92) is an official Apple over-the-air update for the iPhone 6s+, released on 2018-10-30T17:17:11Z. The update package is 1.39 GB. 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: 15016f3c58e9a11183a7cc352eefb89cf2931b1b.zip.