watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 4 (40mm), released on 2019-05-15T17:12:29Z. The update package is 453.59 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2c31d3a4f02ddd81c77d203e8671877698efbcdb.zip.