You can download and install a beta version of Android 8.1.0 on your Google Pixel device if you have such. On my regular Pixel it is marked as OPP5.170921.005. Note that it is a pre-release version. So it may have bugs and glitches.
How to Install Android 8.1.0
First, you need to enroll your device into beta program. Go to https://www.android.com/beta. Type your Google login and password. In a few seconds you should see your device if you have eligible ones. All you need to do here is Enroll your device into the beta program.
Once you’ve done with the enrollment, go to Settings > System > System updates and tap Check for update. You should be proposed to download and install Android 8.1.0 on your Pixel device”