The feature called Always On Display is not new in the smartphone arena. We have been seeing this feature exist in many premium and flagship smartphones such as Moto X, Samsung Galaxy S7/S7 edge, etc.
The highlight of the Always On Display is the ability to have the display enabled but display just a little information to show you the updates. This benefit of this technology is that it lets the screen be efficient without consuming a lot of the battery power. Now, it looks like the Google Pixel smartphone might get the Always On Display anytime soon.
In a recent development, those at XDA seem to have spotted the markings of an Always On Display feature inside the third developer preview of the upcoming Android O update. Some code seems to have tipped at an "always on" doze mode. While this could be confusing, it is said that the doze in the code refers to the Ambient Display feature of Android. Otherwise, it refers to the battery saving Doze mode.
As yet, this feature is not available in the interface. Editing the code in order to turn it on does not add or modify anything. Even if it were to show, it will be categorized as experimental under the hidden UI Tuner settings, showing that it should be brought in by Android O and will not be enabled by default.
This feature is believed to incur some extent of battery drain. This feature could have been included at the beginning itself but if Google does not push through, there will be numerous ways to get the same via the third-party apps.