Remember that Nexus 5X/6P users can’t get automatic WiFi wake-up when the Android 8.0 Oreo update is released? This feature was released for the Pixel series when the Oreo was released, which automatically activates the WiFi connection to a saved high-quality network. Not all Android Oreo devices have this feature, and activation depends entirely on the phone OEM. But in the future, all devices running Android 9 Pie will get this feature.
With the release of the official version of Android 9 Pie and the code of AOSP, the xda-developers dug deeper into the code and said that default would enable all devices that are shipped or upgraded to Android 9 Pie. In the AOSP framework, the value of the config_wifi_wakeup_available function has been changed from 0 (false) to 1 (true), and subsequent commits remove this tag, meaning that default in Android 9 will activate it.
If you compare the config.xml of the Android framework/base branch in the android-8.1.0_r43 tag and the android-9.0.0_r3 tag, you will see that “Turn on Wi-Fi Automatically” has been removed, even if based on Android Pie. Custom ROM also enables this feature by default.
Android 8.0 adds support for WLAN awareness, which is based on the Perimeter-Aware Networking (NAN) specification. On devices with the appropriate WLAN-aware hardware, applications and nearby devices can search and communicate over WLAN without relying on an Internet access point. When Wi-Fi awareness is turned on, the WiFi access point is automatically used when we are near a saved WiFi connection.