Provided GrapheneOS is cleared by Google to launch it as an "Android" device. Given the kind of changes GrapheneOS packs, it may or may not meet Android's mandatory CCD (compatibility) requirements.
It's not their own phone. It's an OEM phone that will be supported by GrapheneOS by flashing it. Once you do it, there's no reason to believe it wont have the same play integrity issues that it currently has on pixel devices.
The Play Integrity shenanigans is mostly on app developers.
That said, good thing GrapheneOS will launch its own Android phone: https://discuss.grapheneos.org/d/27687-new-manufacturer-theo... / https://piunikaweb.com/2025/10/13/grapheneos-ending-pixel-ex... / https://www.androidauthority.com/grapheneos-phone-wait-or-bu...
Provided GrapheneOS is cleared by Google to launch it as an "Android" device. Given the kind of changes GrapheneOS packs, it may or may not meet Android's mandatory CCD (compatibility) requirements.