Google is only beginning the ramp to distributing Android 8.1 to all Pixel and Nexus devices right now, but if you’d rather hurry the process along, you can flash either factory or OTA images right now. Keep in mind that regardless of which one you flash, you’ll want to back up your data as the process wipes all data off the device.
For the first time in a while, we do not see more than one build per device as to serve different carrier or regional subsets. In fact, every eligible device — Nexus 5X, Nexus 6P, Pixel, Pixel XL, Pixel C, Pixel 2, Pixel 2 XL — are receiving one image all together: OPM1.171019.011. Talk about streamlining.
Of course, if you can wait up for the over-the-air image to get sent to you, you can save yourself the work.