watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2021-01-26T18:26:38Z. The update package is 485.36 MB. This is a delta (partial) update that requires 5.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 08ecaec815eeac5130bfafb930a740c495606cca.zip.