iOS 11.4 (build 15F5061d) is an official Apple over-the-air update for the iPhone SE, released on 2018-05-01T17:06:09Z. The update package is 214.5 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: f530f6df7d9be3a8f30ffa3c088d60dc2d43f03e.zip.