watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-08-26T17:15:54Z. The update package is 218.76 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: 590de7d16e6612febc00f8f303066e44c54d1774.zip.