iPadOS 8.4.1 (build 12H321) is an official Apple over-the-air update for the iPad 4 (WiFi), released on 2015-08-13T18:05:09Z. The update package is 40.22 MB. This is a delta (partial) update that requires 8.4 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 3ad842b2a5d4434a71004a2587fc8e8d7c5e826f.zip.