Everyone is asking? What took so long?! Google has finally announced a beta of a new ad unit designed for responsive designed web pages.

In the past, Google said you can modify your ad code to make it work for responsive design web pages, but now, you have the option of using a native AdSense ad unit specifically for responsive design web pages.

To access this, go to your AdSense console, login and create a new ad unit. Then from the drop down of ad sizes, select "Responsive ad unit (BETA)." Yes, Google warns this is a beta.

For most serious publishers, they have already come up with a hacked solution to make their AdSense ad units work on responsive designed web sites or avoided it. But now, many will begin exploring this new beta option.

Google does warn:

Be sure to specify fixed pixel values when setting the width and height of the ad to be served.

Make sure that the specified width and height match one of our supported ad sizes. Please note that link unit sizes aren’t supported at the moment.

The new ad code is responsive on initial page load only. Subsequent changes to the ad size, such as a screen orientation change, will not cause a new ad to be displayed. We know that this is an important feature for many of you and we’re currently working to address this.

Always set a default ad size in case some media queries aren’t supported.

Forum discussion at Google+ & WebmasterWorld.