watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-08-26T17:16:17Z. The update package is 189.37 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 31eed834b425ac20639f31718f82d31d44955518.zip.