The AirPort Extreme Base Station with 802.11n* and Firmware 7.2.1 is Wi-Fi certified for 802.11n* draft 2.0. This update also includes bug fixes and security updates.
This update requires AirPort Utility 5.1 or later. If you have AirPort Utility 5.0 installed, you can update to AirPort Utility 5.2.1 by installing AirPort Base Station Update 2007-002:
AirPort Base Station Update 2007-002 for Mac
AirPort Utility 5.x can be installed using the installation CD included with the AirPort Extreme Base Station with 802.11n*.
System Requirements
Airport Utility 5.1 or later
AirPort Extreme Base Station with 802.11n*
Author's Site