In a significant move, Google rolled out CPM bidding by viewable impression in AdWords this week.
Advertisers will only be charged for ad impressions that can actually be viewed in-screen by users, rather than on the traditional served impression basis.
New reporting metrics are also available, all powered by Google’s viewability measurement solution, Active View, which received MRC accreditation earlier this year. Viewable CPM bidding is available to all campaigns running on the Google Display Network, including remarketing campaigns.
To learn more, read: http://marketingland.com/google-quietly-debuts-viewable-impression-cpm-bidding-in-adwords-66470