watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-07-09T17:20:25Z. The update package is 157.36 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: daf3d05c13dd04a65c5975dad3b22770d06efcc2.zip.