watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-07-09T17:19:31Z. The update package is 137.08 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: 910b31e2e6a4515676c671625d565ac2af01ac88.zip.