watchOS 5.3.1 (build 16U6600) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2019-08-26T17:16:53Z. The update package is 141.91 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3072b9f6d875e491c97ba4c6153b13693c5cba8d.zip.