iOS 9.3.6 (build 13G37) is an official Apple over-the-air update for the iPhone 4s, released on 2019-07-22T17:06:56Z. The update package is 52.4 MB. This is a delta (partial) update that requires 9.3 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: a7c135bf2e46f5167ec77bea938b7be6579fac52.zip.