iOS 9.3.1 (build 13E238) is an official Apple over-the-air update for the iPhone 4s, released on 2016-03-31T16:54:32Z. The update package is 857.09 MB. This is a delta (partial) update that requires 8.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 0a07a024cb6eaa7cff7023b74eb5bd39e7cc873c.zip.