watchOS 5.3 (build 16U5569a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-07-16T17:14:14Z. The update package is 178.32 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ea4c62942d77ff5b727440f0f633156aa362fe10.zip.