watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2019-05-15T17:13:05Z. The update package is 89.73 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: 3ee32341c5ec1b348fdd89b319094068f357b2fe.zip.