Conversion Optimizer beta introduced CPA bidding across search and content

Conversion Optimizer let advertisers set a maximum CPA bid and had AdWords choose a CPC bid for each auction using historical campaign data. Campaigns needed conversion tracking and at least 300 conversions in the previous 30 days, and advertisers were still charged per click.

Google noted it now offered two CPA approaches: Conversion Optimizer on search and content, and the content-only pay-per-action beta.