iOS 9.3.5 (build 13G36) is an official Apple over-the-air update for the iPhone 4s, released on 2016-08-25T16:53:26Z. The update package is 856.13 MB. This is a delta (partial) update that requires 8.4 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 38bb10f6a7998dacb02d4508a1c3c3544e8e6c47.zip.