watchOS 27.0.1 arrived on Sept. 23 for Apple Watch Series 12 and Ultra 4 only, targeting a bug Apple says could cause unexpected restarts.
The patch came five days after those models went on sale and does not extend to other watchOS 27 devices such as Series 9, Series 10, SE 3 or Ultra 2.
Apple has not disclosed what triggers the reboots, how widespread they were, or whether any workout or health-tracking data was lost when a watch restarted.
Series 12 and Ultra 4 owners can install the update from Software Update on the watch or paired iPhone; the watch must be on its charger and above 50% battery.