On Monday, Google has begun updating Google Pixel devices all the way back to the Pixel 2 with the latest May security patch. Unfortunately, Google did not post any specific details as to what the update addresses other than fixes critical bugs and improves the performance and stability of your device.
We were able to pull the OTA on a Google Pixel 4 XL and its only 8.8MB in size. We dont imagine anyone is rushing to download and manually flash the full-size images, but if you are the builds ending in A3 are intended for anywhere outside of Taiwan, build numbers ending in B2 or B3 are intended for Taiwan.
Update arriving on Google Pixel 4 XL
You can always check for the OTA update by heading into the Settings > System > Advanced > System update.