watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-06-11T17:14:18Z. The update package is 475.44 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b4522c07b643add08f9e3a6e6d7c3a0df560576a.zip.