iOS 9.1 (build 13B5130b) is an official Apple over-the-air update for the iPhone 4s, released on 2015-09-30T17:58:10Z. The update package is 148.58 MB. This is a delta (partial) update that requires 9.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b7cac7582ba9b40fae1481adc5c496f26e04c567.zip.