iOS 11.4 (build 15F79) is an official Apple over-the-air update for the iPhone 6s+, released on 2018-05-29T17:16:43Z. The update package is 688.53 MB. This is a delta (partial) update that requires 11.2.6 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 98b0ddd24ab5c0e1c7ddfda78ce888e55ef2912f.zip.