Although it’s hidden, probably set to officially launch with the Pixel 2 duo, it turns out that you can actually enable Always On Ambient Display mode on your Android Oreo ROM with a simple tweak.
Ever since the release of Android O Developer Preview 3, there have been speculations regarding whether Google would finally be bringing a native Always On Display mode to its OS. Unfortunately, among the myriad of exciting features that Android 8.0 Oreo brought – including Project Treble, Notification Dots, and a revamped notification bar – AOD was nowhere to be found. Well, it turns out, Android Oreo actually retains its support for AOD; it’s just tucked away and disabled for now.

According to XDA-Developers, if your phone is rooted and running on an Android Oreo ROM, you can make a simple modification to the commit found under “AmbientDisplayConfiguration.java.” Essentially, the AOD feature is there but is hard-coded to be not visible within settings because it “does not work properly yet.” Once you change the “false” to “true,” however, you should see the option to enable Always On Ambient Display inside System UI Tuner. There are multiple unofficial ports available on XDA-Developers, some of which have this enabled already.