watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-07-09T17:19:45Z. The update package is 118.32 MB. This is a delta (partial) update that requires 5.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d5c6e480447b181311d03c5349442d73fa141408.zip.