As noted by the news release from CalyxOS and Mastodon thread from GrapheneOS, Google did not release the Pixel device-specific source code alongside their Android 16 AOSP release like they usually do. I think many of us, including myself, are hoping this will be published in the near future, but considering they moved AOSP development behind closed doors earlier this year, it’s more likely Google has stopped publishing this section or their code altogether, making development of custom ROMs for Pixel devices significantly more difficult. Sad news for the Android ecosystem, and for open source in general.
I can’t speak to beef, but there is more to Android security than what Google provides. That’s what Graphene is for, to make Android even more secure through hardening various attack surfaces and introducing other completely new security features. If that weren’t the case, Graphene wouldn’t be necessary on Pixels because Google does monthly security patching for them.
It’s also at the firmware level, which Google does not provide except for on their own hardware, and on top of that Google phones are some of the only ones capable of providing some security feature at the hardware level. This seems to be the main thing the Graphene team is trying to point out.