watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2020-12-14T18:08:46Z. The update package is 98.85 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 42a9ba065724f3bbcf6948a2c2dd85b7f6af75ce.zip.