I asked AI: "Do apps loaded onto a Graphene phone through the Google playstore know they are on a Graphene phone?" Answer: Usually, no — not in the simple sense of an app being handed a flag saying “hello, you’re on GrapheneOS now.” On GrapheneOS, Play Store apps and Google Play itself run as ordinary sandboxed apps without special OS privileges, so a normal app does not get some secret built-in “custom ROM detector” API from GrapheneOS. That said, an app can sometimes work it out indirectly. The big one is attestation. GrapheneOS’s own documentation says apps can verify the OS and even explicitly recognise GrapheneOS by using Android hardware attestation and allowing GrapheneOS’s verified boot keys. In other words, an app developer can choose to know. Also, some apps don’t need to identify “GrapheneOS” by name to notice they are not on stock Pixel Android. They may use Play Integrity or similar checks and simply decide the device is “unsupported” or “doesn’t meet policy,” which is why some banking or other apps refuse to run. That is less “I know you are GrapheneOS” and more “you are not the boring default slab I expected.” So the practical answer is: most ordinary apps probably do not explicitly know, unless they are written to check. But yes, apps absolutely can detect or infer it if their developers care enough to implement attestation or fingerprinting logic. GrapheneOS is not pretending to be stock Android with a comedy moustache glued on.