watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-08-26T17:16:24Z. The update package is 120.88 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: 51e2dd747a3f526b80eba8d6867c4c73e4463e6a.zip.