iOS 10.3.1 (build 14E304) is an official Apple over-the-air update for the iPhone 6s, released on 2017-04-03T17:00:35Z. The update package is 583.14 MB. This is a delta (partial) update that requires 10.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 31f57e8322067547e8ad75b4e79648ac6734d0ef.zip.