Just to add to this further this applies to all custom operating systems for Google Pixels not just GrapheneOS.
It was also confirmed by the General Manager of the Android platform that AOSP won’t be going anywhere despite the Pixel build trees being missing for the Android 16 release.
We’re seeing some speculation that AOSP is being discontinued. To be clear, AOSP is NOT going away. AOSP was built on the foundation of being an open platform for device implementations, SoC vendors, and instruction set architectures. AOSP needs a reference target that is flexible, configurable, and affordable – independent of any particular hardware, including those from Google. For years, developers have been building Cuttlefish (available on GitHub as the reference device for AOSP) and GSI targets from source. We continue to make those available for testing and development purposes.