The Android 8.0 release includes Project Treble, a major re-architect of the Android OS framework designed to make it easier, faster, and less costly for manufacturers to update devices to a new version of Android. Treble is for all new devices launching with Android 8.0 and beyond (the new architecture is already running on the Developer Preview for Pixel phones).
Project Treble separates the vendor implementation (device-specific, lower-level software written by silicon manufacturers) from the Android OS framework via a new vendor interface.
https://source.android.com/devices/architecture/treble