According to the document, Google will release the source code for Android 12 on October 4 to the AOSP (Android Open Source Project). AOSP is the place where Google uploads the final builds of Android, from which OEMs like Samsung and OnePlus can take up the code and fit it to their Android skin.
XDA’s Mishaal Rahman says AOSP release dates typically coincide with the ones when Google releases the new Android version to its Pixel devices. Rahman shared a screenshot of the internal Google document that shows the company’s roadmap to stop approving software builds for devices running Android 10, 11, and 12. So, going by the usual release cycle, and the information provided by the document, it’s possible that Google might have set the release date of Android 12 to October 4th.
XDA points Android 12 is taking Google more time than Android 11 and Android 10 to release — both of the previous Android versions were released in September. However, Android 12 comes with new Material You design and many under-the-hood changes which might be taking Google longer than expected.
That said, Android 12 could arrive earlier as well. Samsung is set to release its One UI 4 beta based on Android 12 this month. This could mean Google will release Android 12 to AOSP this month as well.
If you can’t wait for the stable Android 12 build, you can always install the latest Android 12 beta on your phone which is as close to the final thing as possible.