iPadOS 9.1 (build 13B143) is an official Apple over-the-air update for the iPad Air (WiFi), released on 2015-10-21T17:15:54Z. The update package is 235.5 MB. This is a delta (partial) update that requires 9.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d7b1d072aaef1944dfb8aae749dd6176941c49d9.zip.