iPadOS 9.2.1 (build 13D15) is an official Apple over-the-air update for the iPad 4 (WiFi), released on 2016-01-19T17:59:13Z. The update package is 913.4 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: a39c248b076c63722ed9a2732f0ed9648bcd9ee4.zip.