watchOS 5.3.1 (build 16U600) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-08-26T17:16:47Z. The update package is 492.35 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: dbe8619ad66fb4f12fcead334ea2499380b33560.zip.