iOS 9.3.6 (build 13G37) is an official Apple over-the-air update for the iPhone 4s, released on 2019-07-22T17:06:58Z. The update package is 22.81 MB. This is a delta (partial) update that requires 9.3.3 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: e32e6211da3e77c6ba7bb96a4125eca3f2597c88.zip.