CPM algorithm is the Kayzen data science solution to run CPM optimized campaigns on RTB. It optimizes media cost (eCPM) by bidding minimum amount required to achieve desired win rate (desired win rate = 50% per current models).

CPM Bid Optimization optimizes bid values based on fluctuations in floor prices, competition, and request volume throughout the course of a day. 

With CPM Bid Optimization ON, the model will try to achieve a win rate of 50% at or below the target CPM you have set, based on the fluctuations in floor prices.

With CPM Bid Optimization OFF, the campaign will respond with a bid value equal to your Target CPM for all eligible bid requests) (those matching targeting criteria). 

§ CPM Bid Optimization OFF should only be used for highly targeted campaigns in which you know very well the price you're willing to pay for the inventory (i.e. whitelisting a single app, or targeting a small audience)