iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 4s, released on 2016-03-31T16:54:31Z. The update package is 927.68 MB. This is a delta (partial) update that requires 8.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2ebc38850cb7af7e28bfe307ec62897676580ee8.zip.