Unfortunately, Android 12 didn’t drop today on Pixel devices like many expected it would, so here’s the next best thing — Android’s October security patch.
The update is available for the Pixel 3, Pixel 3a, Pixel 4, Pixel 4a, Pixel 4a (5G), Pixel 5, and Pixel 5a devices.
You can check out the October 2021 Android Security Bulletin, here. The bulletin indicates there are no actual updated features and that it offers 20 security fixes. The vulnerabilities range from moderate to critical.
You can download the update over the air or via factory image.
Source: Android Security Bulletin