iOS 10.3.1 (build 14E304) is an official Apple over-the-air update for the iPhone 6+, released on 2017-04-03T17:00:32Z. The update package is 616.81 MB. This is a delta (partial) update that requires 10.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 19479f565832a831bf3efa38c9c65538586a56e1.zip.