Google announced on the AdSense blog that they have a new setting for AdSense publishers to turn on “automated experiments.” It basically lets them opt in to Google testing new AdSense interfaces or features, automatically, to a sub-set of your users, and then you can see how the experiments worked compared to the normal ads.

Google said:

Automatic experiments are experiments that Google runs on your behalf. By allowing Google to experiment with a small percentage of your traffic, you get better and more customized opportunities to help improve your account performance. Opportunities from automatic experiments come with a “verified by experiment” label which means that you can be confident in applying their recommended changes right away.

Forum discussion at Google+.