iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 6, released on 2016-03-31T16:55:19Z. The update package is 1.06 GB. This is a delta (partial) update that requires 8.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: def90e6f9ff9bc7fdef409886e954eb8473ded79.zip.