watchOS 27: Release Date and Every New Feature

watchOS 27 ships Monday, September 14, the same day as iOS 27 and macOS 27 Golden Gate, and arrives just ahead of the new Apple Watch Series 12 and Ultra 4 announced at the September 9 keynote. Unlike iOS 27, which keeps full device compatibility with last year's list, watchOS 27 drops support for several older Apple Watch models.

A New Siri for Your Wrist

watchOS 27 brings the same rebuilt Siri introduced across iOS and macOS this cycle, tuned for quick, on-wrist interactions — faster responses and broader context awareness for things like workout requests, navigation, and quick questions.

Fitness, Health, and a Hidden Readiness App

Health and fitness tracking gets a meaningful expansion this cycle, matching the new sensor hardware in the Series 12 and Ultra 4 — more frequent background heart-rate sampling and broader HRV tracking are both software-enabled features that depend on that new hardware. Code discovered in watchOS 27 betas points to a hidden "Readiness" app, suggesting Apple is building toward a bigger daily-readiness health push, though Apple hasn't detailed it publicly yet.

Smart Stack Improvements

Smart Stack — the context-aware widget stack accessible from the watch face — gains new capabilities this year, surfacing more relevant information automatically based on time of day, location, and activity.

Watch Faces and Everyday Polish

Beyond the headline health and Siri changes, watchOS 27 carries the same visual refinements running across this year's wider software lineup, plus the usual round of small workout-tracking and notification improvements Apple tends to bundle into each yearly release rather than call out individually.

Compatibility: Some Older Watches Left Behind

Unlike iOS 27, which supports the same iPhones as the previous version, watchOS 27 drops support for several older Apple Watch models this year. If you're on an older Watch, it's worth checking Apple's official compatibility list before assuming your device will get this update.

Feature details above are drawn from Apple's own announcement and developer beta documentation. The Readiness app in particular is unconfirmed by Apple directly — sourced to code found in public betas, not an official feature announcement.