They've been moving more and more out of AOSP into their Play Services for a good while now. However I suspect OP was referring to their announcement that they'll require developer verification, and apps to be signed with a certificate they issue, for any app install on a verified device (read any device sold with the Play Store). Long story short, no more building and distributing APKs without Google knowing who you are and that your app exists.

https://android-developers.googleblog.com/2025/08/elevating-android-security.html

[–] Anivia@feddit.org 15 points 4 months ago

There is also the fact that Google used to have a public git with the beta source code of upcoming Android releases, but have recently stopped publishing that source code

https://www.androidauthority.com/google-android-development-aosp-3538503/