iPadOS 8.4 (build 12H4086d) is an official Apple over-the-air update for the iPad Air (Cellular), released on 2015-04-27T17:47:04Z. The update package is 143.04 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: 54c9fb2b18d2d7514d5171a8c5a3b971ed402dc2.zip.