iOS 12.1.3 (build 16D39) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2019-01-22T18:09:32Z. The update package is 1.35 GB. This is a delta (partial) update that requires 11.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a7a5d500d321185e04aff30735dca14aa2f65ac4.zip.