I added updated installation instructions for the new hardened Android Open Source project releases to seamlessupdate.app. Keep in mind these are early sample releases without many changes beyond the new hardened memory allocator for 64-bit. It'll expand in scope over time.
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There are currently sample releases available for the Pixel 2, Pixel 2 XL, Pixel 3 and Pixel 3 XL. There will likely be releases for the Pixel and Pixel XL once time and resources are available to support devices without Android Verified Boot 2.0 again (android.googlesource.com/platform/exter).
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Other devices could also be supported. The Pixel 3 Lite and Pixel 3 Lite XL are likely candidates. Some Android One could potentially be supported as less secure options since some other devices like the Xiaomi Mi A2 appear to support verified boot and attestation for other OSes.
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It takes substantial resources to test releases for each device and to fix the uncovered problems. Many of the memory corruption bugs are in drivers/libraries/services not shared across all devices. Some of the hardening work is also fairly device specific for similar reasons.
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By testing I mean running the whole Compatibility Test Suite and Vendor Test Suite along with the supplementary manual tests for the CTS. It ends up being a huge amount of work to run all the tests while supervising it to record useful information and run some tests again.

