watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2021-01-26T18:26:25Z. The update package is 173.84 MB. This is a delta (partial) update that requires 5.2 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 5ce2028f0d5be4cad0dd1e8b395858e52c063dbd.zip.