watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-08-26T17:16:55Z. The update package is 96.55 MB. This is a delta (partial) update that requires 5.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 355f5022059fc0a3fb14a230842cccab1b2a5c69.zip.