watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-08-26T17:16:49Z. The update package is 143.88 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: 37338225f2b70a24ea2d9a60e5c02795c12984fe.zip.