iPadOS 11.4 (build 15F79) is an official Apple over-the-air update for the iPad Air (WiFi), released on 2018-05-29T17:13:04Z. The update package is 586.7 MB. This is a delta (partial) update that requires 11.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 914f6447c97504a46146230756659bae764c9e07.zip.