You should probably be asking Android OEMs why the requirements listed here https://grapheneos.org/faq#future-devices are unreasonable.

There are currently no other devices meeting the update and security requirements. GrapheneOS is partnered with a major Android OEM working on making devices meeting all of those requirements along with providing official GrapheneOS support. The devices are planned for 2027 but is being announced by the OEM in March 2026 so people will know which OEM it is soon.

Good news they are making their own devices. But until then pixels are technically the most secure android devices and graphene would not be as robust on other devices.

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