watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-05-15T17:11:50Z. The update package is 468.97 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7c29b90cbd4e6f48110d8208122e8cac72b7f0fa.zip.