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.
Enabling this feature allows us to run automatic experiments on a small portion of your traffic and provide you with insightful data about which ads perform best on your site. This could help you optimize your ads and potentially increase your long-term revenue and user engagement on your site**.
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+.