watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-08-26T17:15:07Z. The update package is 139.63 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: 2cf521d0d9e9b173496c3f5557841e0688915e42.zip.