watchOS 5.3.4 (build 16U627) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2019-12-10T18:22:24Z. The update package is 66.26 MB. This is a delta (partial) update that requires 5.3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b67ddd8c20bf3e66c22d766ab4465fdb25c7747d.zip.