watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-08-26T17:17:17Z. The update package is 103.75 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: 1a251667b9aec8ac7636a88aceeac0118a4a0ca6.zip.