Google’s Pixel 3 and Pixel 3 XL are not covered by it even though it currently offers a longer support window because they were released before it was announced. As a result, their software support was supposed to terminate in November of the previous year. Google nevertheless continued to upgrade these smartphones in January and February.
The release that was distributed in February was anticipated to be the final one that these phones would ever receive, but Google like surprising people, so it is continuing to distribute updates to the Pixel 3 and 3 XL. If you intend to use them for a few more years, this is undoubtedly the final instruction they will ever receive.
This is due to the addition of VoLTE roaming functionality, which will be useful when carriers discontinue their 3G networks. There are two builds available; SP1A.210812.016.C2 is for everyone else and SP1A.210812.016.B2 is for people who use Telstra, Optus, or Vodafone Australia for a Pixel 3 or 3 XL. Don’t expect to see the June security patches deployed either because it’s likely that the VoLTE roaming support is the only item contained in this update.
The Google software rollout will presumably take several days to reach all devices, as it always does. You can manually check the system update by navigating to Settings > System > Advanced > System update if you have a Pixel 3 or Pixel 3 XL and are eager.