watchOS 6.3 (build 17U208) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2020-12-14T18:09:07Z. The update package is 147.37 MB. This is a delta (partial) update that requires 6.2.5 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 603381e97ac0d8e2c13aa035e358c4ca977fa1dc.zip.