Today is the "official" launch date of Google's latest flagship phones, so naturally, there are Pie factory images to go along with them. You can download images and OTA files for both the Pixel 3 and 3 XL onGoogle's developer site.
There are two downloads each for the Pixel 3 (Blueline) and Pixel 3 XL (Crosshatch). There's a regular software build and one intended for Verizon phones. Over on the OTA page, you get the same setup with Verizon and standard builds (these won't do you much good right now). Factory images can install over top of anything, but you need an unlocked bootloader. The OTA files can upgrade your device from a previous official build, and the bootloader can be locked.