watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-08-26T17:16:16Z. The update package is 485.29 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f46585c9524eb4aacb75d3b216595774f6405027.zip.