http://wccftech.com/google-android-8-1-developer-preview/

Google has released the Android 8.1 Developer Preview with factory images and OTA files. It is now available for download through the Android Beta Program. The final release is expected to come in the coming weeks for the compatible Nexus and Pixel devices.

There are two developer previews for Android 8.1. The one released today is a beta version with final API, the second preview will come out in November alongside the final system images. The final version for the Android 8.1. will release in December to AOSP and OEM. This version brings Pixel Visual Core features for the Pixel 2 and Pixel 2 XL smartphone along with a slew of new features, bringing it to API level 27. Additionally, there is a new Neural networks API for hardware to bring support for on-device machine learning.