The Google over IPv6 program allows ISPs with good connectivity to request IPv6 access for most Google services. In about a week, we’ll be adding Google App Engine and the appspot.com domain to this program. This means that all App Engine apps will become accessible over IPv6 to anyone participating in the program!
For most people, this won’t require any changes to your code at all. If your App Engine code reads os.environ[“REMOTE_ADDR”] in Python, or HttpServletRequest.getRemoteAddr() in Java, be aware that this value may be an IPv4 address, like “192.0.2.1”, or an IPv6 address, like “2001:db8::1”. Now is the time to verify that your code doesn’t make any IPv4-specific assumptions, so that your IPv6-ready users will have a seamless transition.
More info on http://googleappengine.blogspot.com