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 814.54 MB. This is a delta (partial) update that requires 8.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c41bdeb76e8f68f6b5015965b4be43a1ba68f1ef.zip.