watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2021-01-26T18:26:55Z. The update package is 144.23 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: c1cd9fdfa38af4789fd5a2b71f1e1a045d1f144f.zip.