iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 6, released on 2016-03-31T16:55:21Z. The update package is 300.8 MB. This is a delta (partial) update that requires 9.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 40237b489289910937c53843664f3b205fe41ce7.zip.