App Engine uses four anycast IP addresses:

https://www.bing.com/search?q=ip%3A216.239.32.21

https://www.bing.com/search?q=ip%3A216.239.34.21

https://www.bing.com/search?q=ip%3A216.239.36.21

https://www.bing.com/search?q=ip%3A216.239.38.21