iOS 9.3.6 (build 13G37) is an official Apple over-the-air update for the iPhone 4s, released on 2019-07-22T17:06:50Z. The update package is 933.1 MB. This is a delta (partial) update that requires 8.0 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 6f49abb69af0d0bf13c0c990ffc17a596ede2e74.zip.