watchOS 6.3.1 (build 17U224) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2026-02-02T18:44:41Z. The update package is 556.21 MB. This is a delta (partial) update that requires 6.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 18a4d59ec4594ff5fa0d1f18583b7ca581f5d999.zip.