Android Developers (via Android Police):
For Pixel 6, Pixel 6 Pro, and Pixel 6a devices, Android 13 included a bootloader update to address potential security vulnerabilities, and the anti-rollback counter for those devices was incremented, preventing them from being rolled back to Android 12.
To facilitate app development and testing, we provide modified Android 12 system images for these Pixel devices called Developer Support images. Developer Support images are system images that are based on stable, public builds of Android 12 (API level 31) and the 12L feature drop (API level 32) that also include an updated version of the bootloader with security fixes and an incremented anti-rollback counter.
Great to see Google addressing an issue that had the potential to cause grief for many Android developers using Pixels as test devices. Worth noting though that these are custom system images containing the updated bootloader version – once a Pixel is updated to Android 13, you still won’t be able to run the original, public versions of Android 12 on the device.
Flashing back and forth between these developer support images and the public Android 13 images will also require a full device reset, wiping all data on the device. So you’ll want to backup anything worth keeping prior to doing so.
Also worth noting that OTA security updates won’t be made available in these Developer Support images, and they are not approved for the Compatibility Test Suite.