iOS 12.1.1 (build 16C50) is an official Apple over-the-air update for the iPhone 6s, released on 2018-12-05T18:10:51Z. The update package is 1.34 GB. This is a delta (partial) update that requires 11.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: fc8c157d8142be636de59cd6bb6221bcfebeedb5.zip.