On Monday, Apple released watchOS 9, the latest version of the watchOS operating system designed to run on newer Apple watch models. 

Sleep tracking in watchOS 9 includes sleep staging. Using signals from the accelerometer and heart rate sensor, an Apple watch can now estimate when users are in REM, core, or deep sleep, and when they are awake. Users will see sleep stage data on Apple watch in the app and can view more detailed information, like time asleep, alongside additional metrics, like heart rate and respiratory rate, in sleep comparison charts in the health app on iPhone.

“The sleep experience on Apple watch already empowers users to create wind-down and bedtime schedules, as well as track their sleep to help them meet their goals,” according to a statement from Apple.

The machine learning models were trained and validated against the clinical gold standard, polysomnography, with a large and diverse population.

As the science of sleep is still being explored, users will be able to aid in potential discoveries by contributing their sleep stage data in the Apple Heart and Movement Study through the research app, according to Apple.

Additionally, the new medication tracking feature on Apple watch and iPhone helps users manage and track their medications, vitamins, and supplements, allowing them to create a medication list, set up schedules and reminders, and view information on their medications in the health app.

Custom schedules can be created for each medication, whether it needs to be taken multiple times a day, once a week, or as needed, and users can set up reminders to help keep them on track. In the United States, users can quickly add medications using their iPhone camera, and receive an alert if there are potential critical interactions with medications they have added to the health app.

WatchOS 8 is compatible with the Apple watch Series 4 and later.