iOS 9.1 (build 13B143) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2015-10-21T17:16:03Z. The update package is 1019.55 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: 818f25e7e55bec25e64ccb224251e0807914989d.zip.