tarbeez
Only Pixel hardware on stock OS have had QPR1 since Google didn't release the source code (until just now). Other OEMs haven't had access to it.
I believe this is incorrect. "OEMs that license GMS receive prerelease access to the source code for the next Android version, enabling companies like Samsung to release their Android 16 betas early." https://www.androidauthority.com/android-16-source-code-3563703/
GrapheneOS has also said that they anticipate getting early access to future quarterly and yearly AOSP releases.