First Monday of the month equals a security update for the Pixel devices. Google is now rolling out the May security patch to its Pixel phones.
The company hasn’t posted any specific details as to what the update addresses other than “fixes critical bugs and improves the performance and stability of your device.”
The OTA for Google Pixel 4 XL is 8.8MB in size. You can check for the update by going to the Settings > System > Advanced > System update.