iOS 11.4 (build 15F5071a) is an official Apple over-the-air update for the iPhone 6, released on 2018-05-07T17:11:46Z. The update package is 275.95 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: 80529bf3b92d59816ee2e01ca2dc14fb6264f21b.zip.