watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2020-12-14T18:08:45Z. The update package is 451.79 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 8499a0fdfc8886d43d4183c59b0c4d54cd6dc171.zip.