Apple (MacRumors):

The new Health Sensing System on Apple Watch Series 12 and Apple Watch Ultra 4 features new optical and electrical heart sensors, enabling higher-frequency heart rate and heart rate variability (HRV) measurements, a new readiness score, a more comprehensive Vitals overview with the addition of HRV, and an updated Heart Rate app.

[…]

Apple Watch Series 12 and Apple Watch Ultra 4 introduce readiness — a new feature that analyzes a user’s recent activity, vitals, and sleep score, and then provides a single 0-10 score each day with a clear, actionable recommendation: Recover, Pace Yourself, Ready, or Go For It. This helps a user decide how to take on their workday or tackle their training plan.

[…]

A new Longevity tab analyzes a user’s longitudinal health data for deeper insights into heart health, sleep, mental wellbeing, movement health, metabolic health, hearing, and nutrition. The tab includes Health Age, a new feature that uses Apple Watch data to show users how their metrics are tracking relative to their chronological age, informed by the best available science.

Kuba Suder:

I wonder how much of this new health stuff will work with older / SE watches… probably not much?

Previously:

• Apple Watch Ultra 4
• Apple Watch Series 12

Juli Clover:

Google Health (previously the Fitbit app) collects fitness, sleep, and wellness data from a connected wearable device. Steps, distance traveled, heart rate, sleep, and more can now be added to Apple Health. As noted on Reddit, some data such as HRV doesn't transfer over.

[…]

Syncing can be enabled after downloading the update by selecting Connections, choosing Apps and services, and then adding Apple Health.

My wife is a longtime Fitbit user. A few weeks ago, some family and friends started a friendly competition to see who could get the most steps. They’re all Fitbit users, too. Then she wanted to start comparing step counts with me, but I have an Apple Watch. I thought this would be no problem because the Health app has a sharing feature, and Fitbit and HealthKit have both been around forever. I was shocked to learn that there has never been any syncing. I don’t really understand the reason for this, as it seems like it would make the Fitbit more valuable.

It looks like the syncing part is now solved, but we still can’t automatically compare our steps. We’ve both tried inviting each other to share step counts and some other metrics multiple times over the last several weeks, and it has never worked. Either the invitation doesn’t arrive or the app just spins forever when trying to accept it.

Previously:

• Google Acquires Fitbit