iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 6s+, released on 2016-03-31T16:55:25Z. The update package is 353.5 MB. This is a delta (partial) update that requires 9.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 1bc067a6a24b8f76dfe2a7c839623281abc3fa99.zip.