iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-03-29T17:11:44Z. The update package is 761.39 MB. This is a delta (partial) update that requires 11.0.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2f4ff87693ba80b9ee5f2858aaefa68cc1e761d7.zip.