watchOS 5.3.9 (build 16U693) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2021-01-26T18:26:54Z. The update package is 454.95 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 42cbf61d125b8f6556a7600d3e6f87a97b6c4966.zip.