(VIDEO) Apple Watch Ultra 4 Review: 50-Hour Battery, New Readiness Score Headline First Impressions

CUPERTINO, Calif. — Apple unveiled the Apple Watch Ultra 4 this week, introducing a significantly overhauled health sensor system, extended battery life and a new daily "Readiness" score, while keeping the device's physical design and $799 starting price unchanged from its predecessor.

The watch, announced alongside the Apple Watch Series 12 at Apple's Sept. 9 "Surprise and Shine" event, is available for preorder now, with retail availability and deliveries beginning Sept. 18. According to Apple, the Ultra 4 retains the same physical dimensions, all-titanium case, 3,000-nit peak brightness display and 100-meter water resistance as the Ultra 3, making its most significant improvements largely invisible from the outside.

The centerpiece of this year's upgrade is a completely redesigned health sensing system built around larger, more power-efficient green LEDs in the watch's optical heart sensor, paired with the new S11 chip, Apple's most powerful wearable processor to date. According to Apple, that combination allows the Ultra 4 to measure heart rate every five seconds, a 60-fold increase in sampling frequency compared with the Ultra 3, while heart rate variability is now measured up to every five minutes, a 24-fold increase over the prior generation.

Kaiann Drance, Apple's vice president of worldwide Apple Watch product marketing, described the significance of those sensor upgrades in the company's official announcement.

"The new Health Sensing System and S11 chip take Apple Watch Ultra 4 — our most rugged and capable Apple Watch — to the next level, delivering longer battery life, faster charging, and the most accurate heart rate sensing in a wearable," Drance said.

Tom's Guide, which conducted hands-on testing ahead of the device's launch, confirmed Apple's claims regarding sensor accuracy based on the company's own internal testing against both competing wearables and a traditional chest-mounted heart rate monitor. According to Tom's Guide editorial lead Dan Bracaglia, Apple says the Ultra 4 and Series 12, which share the same underlying sensor technology, now rank as the most accurate heart trackers among any wearable currently on the market.

That increased sampling frequency powers the watch's most significant new software feature: Readiness, a daily score ranging from 0 to 10 that analyzes a user's recent activity, training load, sleep quality and vital signs to offer a simple recommendation for how to approach the day ahead, categorized as "Recover," "Pace Yourself," "Ready" or "Go For It." According to Apple, the underlying calculation draws on baseline data from the Apple Heart and Movement Study to help contextualize each user's individual readings.

Battery life saw the most dramatic improvement of any single specification on the Ultra 4. According to TidBITS, everyday battery life climbed from 42 hours on the Ultra 3 to 50 hours on the new model, while Low Power Mode extended from 72 hours to 84 hours. A new Max Extended Workout mode allows the watch to track outdoor runs, walks and hikes for up to 45 hours while still taking GPS readings every second, giving endurance athletes and backcountry users significantly more tracking capability during extended activities without needing to recharge.

Beyond health monitoring, the Ultra 4 also introduces a new set of Audio Intelligence features enabled by the S11 chip's dedicated, hardware-isolated Secure Exclave, according to Appleosophy. These include Live Rewind, which generates a short text transcript of the previous 15 seconds of speech with a double press of the Digital Crown, and Siri Recap, which summarizes recent conversations without storing the underlying raw audio, reflecting Apple's continued emphasis on processing sensitive data on-device rather than in the cloud. Some of these Audio Intelligence features are not expected to become available until later in 2026, following the watch's initial launch.

The Ultra 4 also ships with support for Apple's newly redesigned Siri AI assistant, part of the broader iOS 27 and watchOS 27 software ecosystem Apple introduced alongside its new hardware this week. A pedometer algorithm rebuilt using machine learning on the S11 chip is intended to deliver more accurate real-time step counts and distance tracking during outdoor workouts, according to Neowin's coverage of the announcement.

Despite the substantial internal upgrades, some early coverage has noted specific limitations that did not make it into this year's model. According to SmartBodyTouch, the Ultra 4 does not include cuff-accurate blood pressure monitoring or non-invasive blood glucose tracking, two features that had been the subject of speculation ahead of the announcement. DigiTimes had previously reported that Apple submitted a more advanced real-time blood pressure alert feature for U.S. Food and Drug Administration review, though whether or when that specific capability might eventually ship remains dependent on regulatory clearance rather than a confirmed feature of the current Ultra 4 hardware.

A redesigned Health app on iPhone is set to arrive later this year alongside the new hardware, introducing a new Longevity tab featuring a Health Age metric that compares a user's tracked health data against age-based benchmarks, according to MacDailyNews' coverage of the announcement.

For prospective buyers weighing whether to upgrade, SmartBodyTouch's early assessment characterized the Ultra 4 as representing the most substantial update to the Ultra lineup since its original 2022 launch, driven primarily by the expanded sensor array and its downstream software features rather than any change to the watch's external design. The outlet suggested the upgrade would prove most compelling for users currently on an Ultra 2 or the original Ultra model, while recommending that current Ultra 3 owners consider skipping this particular generation given the relatively modest physical changes involved.

With the Apple Watch Ultra 4 now available for preorder at its unchanged $799 starting price and set to begin shipping Sept. 18, the device's real-world performance, particularly the accuracy of its redesigned health sensors and the practical usefulness of its new Readiness score, will become clearer once independent reviewers and early adopters have had the opportunity to test the watch extensively following its retail launch later this month.