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 end in November of the previous year. Google nevertheless continued to update these devices in January and February.
The build that was distributed in February was anticipated to be the final one that these phones would ever receive, but Google enjoys 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 last instruction they will ever receive.
This is due to the addition of VoLTE roaming support, 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 those who use Telstra, Optus, or Vodafone Australia for their Pixel 3 or 3 XL. Don't expect to see the June security patches applied either because it's likely that the VoLTE roaming support is the only thing contained in this update.
The Google software rollout will probably take several days to reach all devices, as it usually does. You can manually check the system update by going to Settings > System > Advanced > System update if you have a Pixel 3 or Pixel 3 XL and are impatient.
