watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-07-09T17:19:38Z. The update package is 111.25 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: 44dd3bfab143995943315125b0a1797deeaf3e36.zip.