iOS 11.4 (build 15F5049c) is an official Apple over-the-air update for the iPhone 6, released on 2018-04-16T17:08:19Z. The update package is 218.7 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: 338624b21e8a22c9f0b0bcbe6909068bc9795f37.zip.