iOS 12.0 (build 16A366) is an official Apple over-the-air update for the iPhone 6s, released on 2018-09-12T19:11:35Z. The update package is 1.28 GB. This is a delta (partial) update that requires 11.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d2aaf16863c675dddaccbcf34a5b90ea2bb2a005.zip.