watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-06-11T17:14:20Z. The update package is 146.63 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: df98c85e8e1fc1dcb554b916dba5dfa739f44ef9.zip.