How does your billing model work? uses multi CDN across the globe with a caching hit ratio of 98%. We only charge for the requests we receive in our cluster (the 2% remaining). We don't charge for any further images served by the CDN edge servers. For example, if you have 75.000 Image Optimization Credits available on your account, you can serve 25.000 master images in 3 different view port sizes. (Desktop, Tablet, Mobile)