watchOS 5.3 (build 16U5537b) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-05-28T17:12:35Z. The update package is 104.82 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: 4a8d3d3c3c6872ef6eba5b8da9fb2dadb21e9665.zip.