Google is getting an early start in 2018 by rolling out the monthly patches for Nexus and Pixel devices. The OTA files and full system images are available a few days earlier than usual, and devices should begin seeing updates in the not too distant future. It looks like several devices have two different builds available this month, so you'll have to grab the right one if you just can't wait.
As usual, the OTA files are live for those of you without an unlocked bootloader. You can install these with ADB sideload on top of the current official software—no data wipe needed. System images can be flashed on top of anything, but they require an unlocked bootloader and include a data wipe by default. Skip that at your own risk.
All the Pixel phones have a standard Oreo build as well as a separate build for use on O2 in the UK. We don't know what's different about that version, but we do have the basic patch details. The security bulletin is live if you want to see which vulnerabilities are addressed. The Pixel-specific bulletin still hasn't been updated for December, so there's no telling when or if Google will post this month's.