iOS 9.3.6 (build 13G37) is an official Apple over-the-air update for the iPhone 4s, released on 2019-07-22T17:06:55Z. The update package is 228.17 MB. This is a delta (partial) update that requires 9.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: c3d27116d72d47889bc752c8b014e431aa3fa32e.zip.