They said they're going to merge their private branch after their full releases, as opposed to merging many times on the way to a release.

https://9to5google.com/2025/03/26/google-android-aosp-develo...

> This does not mean that Google is making Android a closed-source platform, but rather that the open-source aspect will only be released when a new branch is released to AOSP with those changes, including when new full versions or maintenance releases are finished.