watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-05-15T17:11:51Z. The update package is 148.36 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 37dbc8d4ec1dabaf4cfd9364c4e0f8178c88dab6.zip.