iPadOS 8.4 (build 12H143) is an official Apple over-the-air update for the iPad Air 2 (Cellular), released on 2015-06-30T15:51:17Z. The update package is 210.31 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: 151aa9ad4d71613ef63c9800c9e589873615a4b7.zip.