iPadOS 9.1 (build 13B143) is an official Apple over-the-air update for the iPad 2 (WiFi), released on 2015-10-21T17:15:48Z. The update package is 736.09 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: e78cd528dca5186265284f415f53cf46039fc7b5.zip.