Not every Apple Watch will be able to track your sleep — here are the models that Apple just announced will get the new features in the fall

• One of the biggest new features coming to the Apple Watch this fall is sleep-tracking, a capability that rivals like Fitbit had offered for years.
• But the new software update will only be available for the Apple Watch Series 3, Series 4, and Series 5, a departure from Apple's previous approach of launching new software updates for almost every Apple Watch version.
• Hand-washing detection, another new watchOS 7 feature, will only be available for the Series 4 and 5.

Apple is finally bringing sleep tracking to the Apple Watch, a feature that Apple's popular watch had lacked compared to rival devices.

But not every version of the Apple Watch will get the new feature, which will be part of the company's watchOS 7 software update coming in the fall. The new software will be compatible with an Apple Watch Series 3, Apple Watch Series 4, or Apple Watch Series 5 paired with an iPhone 6S or later running iOS 14.

That differs from previous software updates, which were available for the Apple Watch Series 1 and later. Even last year's watchOS 6 update, a release that brought new features like the ability to track activity trends over time and monitor hearing health, was available for all watch models dating back to the Series 1 from 2016.

Apple's new automatic handwashing detection, another new feature coming with watchOS 7, also isn't available on the Apple Watch Series 3 despite the fact that this model supports the software update. That feature will only be compatible with the Apple Watch Series 4 and Apple Watch Series 5 since it needs the more powerful processors found in those newer watches.

It's not necessarily surprising that the update is only available for Apple's newer watches. As Apple develops more advanced features for the Apple Watch, it seems unrealistic to think that they would be able to run on all versions of the watch forever.

But it's still significant considering one of the Apple Watch's best selling points has always been that you don't need to upgrade to the latest model to get all of the newest features. The biggest differences between the $200 Apple Watch Series 3 from 2017 and $400 Series 5 from 2019 in terms of functionality, for example, are hardware-based features like its always-on display, ECG sensor, and fall detection capabilities.

Of course, there are other differences when it comes to design, screen size, and processing power, but for the most part there wasn't much of a discrepancy in terms of functionality.

Other than sleep-tracking and handwashing detection, watchOS 7 will bring the ability to share custom watch faces and new types of workouts, like dance and core training. The public beta will be available starting in July, while the full version will debut in the fall.