iOS 9.3.6 (build 13G37) is an official Apple over-the-air update for the iPhone 4s, released on 2019-07-22T17:06:51Z. The update package is 928.03 MB. This is a delta (partial) update that requires 8.1.2 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: a7a57ccd066373bff5a5d609a6ef9ab68e2140e0.zip.