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 931.6 MB. This is a delta (partial) update that requires 8.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 3eb7e54276cde726d2edb8b615d8d7e5d3aea149.zip.