watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-08-26T17:14:57Z. The update package is 466.96 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: cebe04f6e9c4285ba9fe104d87f485c0b61431da.zip.