Every once in a while, Google mistakenly rolls out software not meant for the public. These dogfood builds contain experimental features the company wants to test internally even before letting them loose on beta users. It seems that such a confidential OTA update rolled out to some Pixel 3 and 3 XL users over the last couple of hours, as we've received word that people already got the November security patch accompanied by a note saying "CONFIDENTIAL INTERNAL ONLY."
Even though this is an internal build, nothing too exciting seems to be going on for users — after all, it's just a test version of a regular security patch. The update notes say the 15.8MB light OTA contains "patches and critical bugfixes." The rest of the information accompanying the build is addressing Googlers: They may use their devices normally but shouldn't "discuss or comment on this update externally."
— Desean (@desean84) October 31, 2019
Once people updated their phones to this internal build, they saw their security patch level raised to November 5, 2019, which is in line with Google's usual update schedule. As far as we can tell, both the Pixel 3 and 3 XL could benefit from this accidental rollout.