iPadOS 8.4.1 (build 12H321) is an official Apple over-the-air update for the iPad 4 (WiFi), released on 2015-08-13T18:05:08Z. The update package is 640.49 MB. This is a delta (partial) update that requires 8.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: e3a54d4207bf66396bf2f49dbe00da5d33cc8d52.zip.