https://wccftech.com/android-8-1-developer-preview-2/

After rolling out the Android 8.0 Oreo stable versions to Pixel and Nexus devices, Google has now released the factory images for Android 8.1 Developer Preview 2. The “Near-final system images for final testing” have been released for the Pixel and Nexus devices. The public launch of the update is just a month away now. The new factory images are on build number OPP6.171019.012 and are compatible with these devices –  Pixel, Pixel XL, Pixel C, Pixel 2, Pixel 2 XL, Nexus 6P, and Nexus 5X.

For the users with any of the aforementioned devices, it is not necessary to sideload the updates (especially when you are new to the sideloading process), you can get Android 8.1 preview by signing up for Google’s Android Beta Program. After signing up for the program, you will have to wait for around two days to receive the OTA update.