Predicted by Bloomberg, the feature is said to be in testing by Apple employees currently. However, as the report expects that it will arrive in the 2020 lineup of products, it is not ready for public use.
The rumored feature addition isn’t a big surprise. Apple acquired sleep monitoring company Beddit in 2017, and revised the product in 2018. It is also a logical extension of the company’s continued push into health monitoring.
Bloomberg notes that addition of sleep tracking would require more battery life, as most users presently charge the device at night.