The launch of the Apple Watch Series 12 and Ultra 4 is one of the most satisfying Apple Watch updates in years. At least it was for me. Four changes have finally arrived that this site has been asking for, testing, or predicting for a long time.
1. HRV is now measured much more often
In June 2026, this site found that Apple Watch took HRV readings opportunistically when the wearer was still, with a gap of around 15 minutes between readings. That produced roughly four minutes of HRV data per hour in testing. The actual frequency varied depending on movement, and any reading rejected due to motion pushed the next attempt further out.
That is insufficient data for readiness scores, training-load adjustments, and recovery recommendations. That;s now hopefully fixed once and for all with AWU4 (probably not backported to AWU3)
| Previous Apple Watch | Series 12 | |
|---|---|---|
| HRV measurement frequency | Opportunistic when still; ~15 min gap between readings in testing | As often as every 5 minutes |
| Data collected per hour | ~4 minutes (site testing; varies by movement) | Up to 12 minutes |
| Risk of missed readings | High (movement rejects reading, extending wait until next attempt) | Lower (more opportunities per hour) |
| Readiness score | Not available | Daily 0–10 score |
Other devices from Whoop, Oura, and Garmin collect much more HRV data overnight.
Bevel has also wanted Apple to collect HRV more frequently, but there was no way for a third-party app to make Apple Watch do that.
Apple has now fixed the problem at the hardware level. Series 12 can measure HRV as often as every five minutes, up to 24 times more frequently than before. The new Readiness app is largely made possible by this increase in data.
2. The sensors are more efficient, which helps battery life
Series 12 increases outdoor workout battery life from 8 hours to 10 hours. That is a whopping 25% improvement, even though everyday battery life is still rated at 24 hours and the sensors now run continuously throughout the day.
| Series 11 | Series 12 | Ultra 3 | Ultra 4 | |
|---|---|---|---|---|
| Everyday use | 24 hrs | 24 hrs | 42 hrs | 50 hrs |
| Outdoor workout | 8 hrs | 10 hrs | 14 hrs | 18 hrs |
| Low Power Mode | 36 hrs | 38 hrs | 72 hrs | 84 hrs |
| 15-min charge | 8 hrs use | 12 hrs use | 12 hrs use | 18 hrs use |
Independent estimates suggest the battery itself is only about 7 to 10% larger, which doesn’t explain the full 25% improvement during workouts. The new sensor uses larger, rectangular LED components that produce more light with less power, along with improved signal-processing software.
The Ultra 4’s 18-hour outdoor workout figure is enough for a full Ironman for most competitors without using Low Power Mode. Apple has positioned the Ultra as an endurance (Ultra!) watch since 2022, but this is the first generation that genuinely delivers on that promise even though hardcore Ultra runners will still find it inadequate. See the Ultra 4 vs Ultra 3 full comparison for the complete details.
What actually changed in the sensor?
Apple describes the new sensor as having a “ring photodiode layout,” which makes it sound like the physical layout is new. It’s not.
| Ultra 3 | Ultra 4 | |
|---|---|---|
| Number of LEDs | 8 | 8 |
| LED arrangement | Ring (two squares of 4, rotated 45°) | Ring (two squares of 4, rotated 45°) |
| LED die shape | Smaller, rounder | Larger, rectangular |
| Power efficiency | Standard | Improved |
Both Ultra 3 and Ultra 4 already had eight LEDs arranged in a ring – one new difference is that Apple has now drawn concentric rings around them! The main physical change is the LEDs themselves. The key improvements are more efficient LEDs and better signal processing, not a completely new ring design. The LEDs also appear larger in some of the early images.
3. Apple dropped GLONASS from Ultra 4
Apple’s Ultra 4 specifications list GPS, Galileo, QZSS, and BeiDou, but it no longer includes GLONASS. Ultra 3 supported GLONASS, and the single-frequency Series 12 still does. This follows a similar move by Garmin with the Fenix 9 Pro just five days earlier. For more background on how satellite constellations affect accuracy, see the GPS accuracy guide.
| Constellation | Ultra 3 | Ultra 4 | Series 12 |
|---|---|---|---|
| GPS | ✓ | ✓ | ✓ |
| GLONASS | ✓ | ✗ | ✓ |
| Galileo | ✓ | ✓ | ✓ |
| QZSS | ✓ | ✓ | ✓ |
| BeiDou | ✓ | ✓ | ✓ |
| Frequency | L1+L5 dual | L1+L5 dual | L1 only |
| Label | Precision dual-frequency | Precision dual-frequency | Precision L1 |
GLONASS is potentially less accurate as a constellation. Dropping it probably decreases the chance of error (or increases accuracy; phrase differently)
Series 12 still supports GLONASS but carries Apple’s new “Precision” L1 label. The name is new, but the underlying hardware isn’t. The “Precision” part refers to Apple’s GNSS sensor fusion, which combines GPS data with accelerometer and gyroscope data to improve positioning, e.g. when going through a tunnel.
4. The chip is finally genuinely new
The S11 is Apple’s new Apple Watch chip, used in both Series 12 and Ultra 4, which incorporates A20 Pro-derived CPU, GPU and Neural Engine elements. Apple does confirm that S11 ends a three-year period in which the watch chip was built around the same basic architecture derived from the A16.
| Model | Chip | Architecture |
|---|---|---|
| Series 9 / Ultra 2 | S9 | Sawtooth (A16-derived) |
| Series 10 | S10 | Sawtooth (A16-derived) |
| Series 11 / Ultra 3 | S10 | Sawtooth (A16-derived) |
| Series 12 / Ultra 4 | S11 | A20 Pro-derived (per 9to5Mac) |
The S11 introduces two efficiency cores, a single-core GPU, a four-core Neural Engine, and a dedicated always-on processor that runs background tasks without draining the battery. The always-on processor lets the sensor collect heart rate and HRV data continuously throughout the day. The Neural Engine’s primary job is continuous Audio Intelligence: Sound Recognition, Live Rewind, and Siri Recap.
What this means for Bevel and Correlate
The biggest winner here may actually be third-party apps. More frequent HRV measurements and a continuously running optical sensor give apps like Bevel and Correlate much more useful data. Their algorithms can only be as good as the data Apple gives them, and that data has now improved significantly.
Both apps also have a downside. Apple’s new Readiness feature now handles the basic recovery and readiness scoring that previously drove people to third-party apps. Bevel still has an important advantage with strength training and gym-focused readiness, areas that Apple’s Readiness feature does not cover. Correlate’s advantage is its ability to work across platforms and devices Apple doesn’t make.
Apple has now added a free built-in feature that users previously needed a third-party subscription to access. For a full breakdown of how Series 12 compares with Series 11, see the Series 12 vs Series 11 comparison. For triathlon-specific battery considerations, see the best triathlon watch guide and the Apple Watch Ultra 3 review.
Quick answers
Why does Apple Watch Series 12 have better battery life during workouts?
Outdoor workout battery life increases from 8 to 10 hours. The battery is estimated to be only about 7 to 10% larger, so that doesn’t explain the full 25% improvement. The new, more efficient LEDs can produce a stronger signal while using less power, and improved software can process that signal more efficiently. Apple has not provided a detailed breakdown.
What changed in the Apple Watch Series 12 optical sensor?
The LEDs are larger and more rectangular, so they produce more light with less power. The basic eight-LED ring design and photodiode arrangement are carried over from previous models. Apple has also improved the software that processes the sensor data.
What does Precision L1 GPS mean on Apple Watch Series 12?
Precision L1 is Apple’s new name for the single-frequency, multi-constellation GPS system in Series 12. The underlying receiver hardware is unchanged from previous Series models. Precision refers to Apple’s software, which combines GPS data with accelerometer and gyroscope information to improve positioning.
Why did Apple drop GLONASS from Ultra 4?
Apple has not confirmed the reason. GLONASS uses a different signal system from the other major satellite constellations, which adds hardware complexity. Removing it simplifies the GPS hardware without meaningfully affecting positioning quality for most users. Garmin made a similar decision with the Fenix 9 Pro shortly before Apple’s announcement.
How often does Apple Watch Series 12 measure HRV?
Series 12 can measure HRV as often as every five minutes. Previous Apple Watch models took readings opportunistically when the wearer was still, with gaps of around 15 minutes between readings in testing, giving roughly four minutes of HRV data per hour overnight. The higher sampling rate provides significantly more data for features such as Readiness and recovery tracking.
For full specs, see the Apple Watch Series 12 specifications and Apple Watch Ultra 4 specifications. For a broader view of recovery tracking options, see the recovery trackers guide and the Whoop guide. For the best Apple Watch for sport, see the buyer’s guide.
Last Updated on 9 September 2026 by the5krunner
My favourite kit and nutrition
- Garmin Fenix 9 Pro — I’ve just bought one.
- Injinji – Runners protect your toes. Avoid discomfort and minor injury. Run more. Run faster. I use them.
- Garmin 90-degree charging adapter — A small keyring adapter you can use anywhere. Essential when away. I use one.
- Garmin charging puck — the fastest and most reliable way to top up your Garmin before a session. I use one.
- Ravemen FR300 — Front light that mounts directly under your Garmin or Wahoo head unit. Keeps your bars clean and your beam pointed where it matters. I use one.
- Body Glide – The blue anti-chafe stick that all swimmers and many runners use. I use it.
- Maurten — The race nutrition trusted by elite athletes. Gels and drink mixes engineered to be easy on the stomach. I use them.
- Garmin Varia RTL515 — A radar rear light that alerts you to vehicles approaching from behind. Pairs with your Edge or Wahoo. I use this model.
- Favero Assioma Pro RS2 — The power-meter pedals most serious cyclists choose. Accurate, easy to move between bikes. I use this model.
- Garmin Forerunner 970 — A serious choice for a pro-grade triathlon watch. I use this.
- Polar H10 — My daily driver for accurate, waking HRV readings.
- Wahoo ELEMNT Roam 3 — The bike computer that has the feature Garmin lacks: usability. I use mine on most rides.
Reader-Powered Content
This content is not sponsored. It’s mostly me behind the labour of love, which is this site, and I appreciate everyone who supports it.
Support the site: Follow (free, fewer ads) · Subscribe (paid, ad-free) · Buy Me A Coffee ❤️
All articles are written by real people, fact-checked, and verified for originality. See the Editorial Policy. FTC: Affiliate Disclosure — some links pay commission. As an Amazon Associate, I earn from qualifying purchases.
tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID
