iOS 9.1 (build 13B143) is an official Apple over-the-air update for the iPhone 4s, released on 2015-10-21T17:15:59Z. The update package is 894.12 MB. This is a delta (partial) update that requires 8.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b761132ff2682983fe3bf8bd8d9e49226530a905.zip.