watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-08-26T17:16:01Z. The update package is 68.03 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: 0fd18799f5d862fb75aff8d66a59ff4c4c7b415e.zip.