The tool is known as AdWords campaign Experiments or ACE. As the name suggests, the tool will allow advertisers to experiment with their campaigns, to test and measure the effect of any changes which they make to keywords, bids, Ad Groups and placements on the performance of the campaign.
Earlier, the best way one could gauge the performance of the ad was by comparing the results obtained before and after the changes were made. But this system was often inaccurate due to various uncontrollable factors such as holidays, weekends, changes to end user and advertiser behaviour.
With ACE, advertisers will be able to have more accurate information, by running the new experimental campaign concurrently with the original campaign. This simultaneous split test will enable advertisers to judge more accurately, the impact of the changes in the ad campaign.
It will be possible to measure the impact of adding new keywords or changing the keyword and Ad Group level. They can also restructure the content campaigns using more tightly themed Ad Groups. They can also check the change in volume by using different keyword match groups, or use an Ad Group default bid versus keyword-level bids etc.
ACE is still in the beta testing stage and Google has invited only their U.S. advertisers who use English to participate in the test.
AdWords Campaign Experiments: Introducing Google’s Split Testing Tool