iOS 11.4 (build 15F5037c) is an official Apple over-the-air update for the iPhone 6+, released on 2018-04-02T17:06:55Z. The update package is 261.17 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 10f250d7acd5d20f8e2c06e6f7db07c675cb9ed7.zip.