iOS 12.1.3 (build 16D39) is an official Apple over-the-air update for the iPhone 6s, released on 2019-01-22T18:10:58Z. The update package is 1.29 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: 07e1dcc7dd5c26bb083f4a81f2727fc6f21ed873.zip.