Today, we're adding the same service to all domains hosted by ghs.google.com. If your App Engine app runs on your own domain name using Google Apps, then be sure to review our earlier blog post, which discusses the caveats of parsing client IP addresses, and how to use the SixXS Gateway to test your site over IPv6.
Currently, the Google over IPv6 program presents AAAA records only to ISPs within our whitelist. This helps ensure that our services remain reliable, by reducing exposure to clients with broken IPv6 connectivity. As the maturity of IPv6 deployment improves, we expect this whitelist to grow, eventually disappearing as it encompasses the entire Internet.
That said, we know that some of you are fans of IPv6 who would prefer to skip the whitelist, and offer dual-stack service to everyone immediately. To make your domain bypass the whitelist, just change your CNAME pointer from ghs.google.com to ghs46.google.com. Please note that, while ghs46 will cause your App Engine site to receive a larger fraction of its traffic over IPv6, our studies show that it may make your site slow or unreachable for up to 0.1% of clients across the Internet, so use this alternate domain with care.