Apple released watchOS 27.0.1 on Wednesday, September 23, 2026, and it exists for one reason. The update fixes a bug that made the Apple Watch Series 12 and Apple Watch Ultra 4 restart on their own. It arrives one week after watchOS 27 shipped.
What the watchOS 27.0.1 restart bug looked like
Owners reported the watch rebooting in the middle of ordinary tasks. The reports covered a fairly wide spread of activities:
- Editing or customising a watch face
- Taking a phone call from the wrist
- Asking Siri something
- Opening Maps or the App Store
- Recording a workout
Apple’s release notes stay generic. They describe the change only as fixing an issue that could cause the watch to restart unexpectedly, with no technical detail about the cause.
A more specific explanation has circulated widely, but it did not come from Apple. A post on Apple’s Developer Forums traced the reboots to a Neural Engine command timing out at 2,020ms against a 2,000ms limit. That is a developer theory, not an Apple-confirmed root cause, and it is worth treating as such until Apple says otherwise.
Which watches get it, and how to install
The update applies to the Apple Watch Series 12 and Apple Watch Ultra 4 only. Older Apple Watch models are not part of this release, which lines up with the bug reports being confined to the two newest devices.
Installing it needs the usual two conditions. The watch has to be on its charger, and the battery has to be above 50%. One user reported a download size of 384MB. Apple has not published a figure of its own, so treat that number as a data point rather than a specification.
Credit where it is due: a week is a fast turnaround for a fix of this kind, and Apple did not leave affected owners waiting through a full point release. The flip side is equally plain. watchOS 27 went out the door with a defect serious enough to interrupt calls and workouts on Apple’s two newest and most expensive watches. If you own a Series 12 or an Ultra 4 and have been putting up with random reboots for the past week, the fix is available now.
Source: MacRumors
