For those who are new to Pixel and want to understand how updates work, here is a Reddit link from couple of years ago which explains the update process. Explains how carriers are involved and how the updates can be delayed for a particular carrier etc. I like to point to this thread every time question about why my update is delayed comes
https://www.reddit.com/r/GooglePixel/comments/7bfkdr/psa_pixelnexus_updates_can_still_be_subject_to/
## Carrier Involvement
Google has agreements with various carriers that allow for certain perks for both sides. One of these perks for the carrier is the ability to review the update for compatibility for that carrier's specific features. And yes, Apple deals with this too. Apple, however, releases their update when EVERY carrier is done (and due to Apple's market position, they get priority in the review process, further speeding this up). Google, on the other hand, pushes the update when it's ready, regardless of carrier status. If your carrier isn't involved, you're eligible for the update. If your carrier has approved the update, then you're eligible for the update. And if your carrier has not yet approved the update, then you are not yet eligible for the update. When the carrier approves it, Google will push it to you.
## Carrier Association, and How it Works
When you first boot up your phone with a carrier's sim installed, that phone becomes associated to that carrier in Google's database. This is NOT a carrier lock, and it is used by Google for identification purposes.
Google maintains this list and, when they push out an update, all phones associated to a carrier that has approved the update, or a carrier that has no role in the process, receive that update. Carriers that have yet to approve the update are not pushed the update.
You can change your carrier association by swapping to a different carrier's sim and rebooting. Or, you can delete your carrier association by powering down, removing the sim (do not reinsert), powering up, and performing a full factory reset. With no sim installed, the fresh phone has no carrier association and will pull the latest available update.