watchOS 6.3 (build 17U208) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2020-12-14T18:09:02Z. The update package is 447.26 MB. This is a delta (partial) update that requires 6.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 69603e8db573e17ea71bedc83b12bf3188e497ea.zip.