watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2019-08-26T17:16:35Z. The update package is 151.43 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: e83ea0beff3c3b4cfd4708799b691edf5c0d08b5.zip.