watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-10-09T17:12:16Z. The update package is 405.08 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 21fa83c292fec8372e3e2ff6804e0e25fe57d24c.zip.