watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-08-26T17:15:41Z. The update package is 118.85 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: 2aa2d269839dc96d85d6ce291c3332595af7b55c.zip.