iPadOS 9.1 (build 13B143) is an official Apple over-the-air update for the iPad 4 (WiFi), released on 2015-10-21T17:15:52Z. The update package is 906.8 MB. This is a delta (partial) update that requires 8.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c10f46c7972a1169f5801291071813d16db24954.zip.