Google released the Android O Developer Preview 4 (build number OP4170623) for supported Pixel and Nexus devices with some significant changes and fixes. This is the last Developer Preview release of the OS before Google releases the final version (Android 8.0) to the public. The final version of Android O (Android 8.0) probably will release by August or September.
Android O DP4 OTA update is starting to roll out and user who signed up for Android Beta Program will get the update soon. This update is called Release Candidate build of Android O and includes latest patches, and the final APIs. It means the update is almost stable and bug free, so anyone can tryout the OS right now, though it is primarily meant for developers.
Besides the Developer Preview 4 release, Google is also releasing the stable version of Android 26.0.0 Support Library and updated versions of the SDK, tools, and Android Emulator system images.
Also, developers can build apps targeted for Android O (Android 8.0) and publish on Play store as alpha, beta, or production channels.
The O Developer Preview is available for Pixel, Pixel XL, Pixel C, Nexus 5X, Nexus 6P, Nexus Player, and the Android Emulator. Android Beta enrolled devices will automatically update to the official version of Android O.