What is the official Gentoo AMI?

I could not find an official build for EC2. The closes thing is likely going to be the Pygoscelis Papua Linux distro.

Dowd and Associates is offering Pygoscelis Papua Linux. Pygoscelis Papua Linux is an unofficial build of Gentoo Linux for Amazon EC2.

You can also peruse the Cloud Market list of images available.

• The Cloud Market Gentoo Images

If you'd rather there are other methods discussed within these resources which cover rolling your own Gentoo image from scratch.

• Gentoo in Cloud
• Gentoo EC2 Tutorial / Bootstrapping
• Multiple WordPress Blogs, Gentoo Linux, and Amazon EC2