watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-05-15T17:13:02Z. The update package is 82.99 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 72215c1c3f06682a168662d3c0979fd11a24dd9c.zip.