iOS 11.4 (build 15F5049c) is an official Apple over-the-air update for the iPhone 6s, released on 2018-04-16T17:08:20Z. The update package is 218.9 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: 158b065d1fc7e54b3ebeaf801389ada6a1990c7b.zip.