iOS 12.1.3 (build 16D39) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2019-01-22T18:09:38Z. The update package is 312.33 MB. This is a delta (partial) update that requires 12.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 01f2128f80a89e0189a46e213f8081f2150e41b4.zip.