Supposedly the AB initially showed as available within the Tesla app for early customers who received an (Austin built) Tesla Model Y with the 4680 battery (Tesla Model Y is the correct model name, not sure why people call it the Standard Range Model Y. In 2021, for ~2 months only, Tesla offered a Standard Range Model Y that was rear wheel drive only.)
It is unclear whether the AB could actually be installed in the current Tesla Model Y with the 4680 battery. AB no longer shows up under upgrades within the Tesla app for those who purchase the Tesla Model Y (AB continues to be available in the Tesla app under Upgrades, after purchase, for $2,000 for the Long Range Model Y and the Long Range Model 3.) It is unknown if or when Tesla will make the AB upgrade available to purchasers of the Tesla Model Y with the 4680 battery.