What is "Max CPM"?

Max CPM is a parameter of the Cost-Per-Day (aka Daily budget) advertising campaign that works as a filter: it excludes the traffic sources with expensive traffic from the campaign's targeting.

If Max CPM is not specified, the default value is used, which works fine in a normal situation and protects advertisers from overpaying for traffic.

However, when multiple big advertisers compete for a single site, they may raise its CPM, thus effectively excluding it from their campaigns' targeting.

Isn't $100,000 too much?

Max CPM is not the traffic price - it is a filter. If you do not want to filter out ad units by CPM, you can set it to the maximum allowed value.

Due to the way how we measure traffic, one IP address can generate only one unique impression per day. So if there are multiple ad units on the same page, the first one will get most of the unique impressions, and the last one may appear to have an insanely high CPM.

It appears that some advertisers are ready to pay over $10,000 per thousand of unique impressions on such ad units, so we decided to increase the maximum allowed value to $100,000.

Why is there even a limitation for "Max CPM"?

It is a sanity check to protect our advertisers from misconfiguring their campaigns. A few months ago, we thought that an over $100 value could be there only by mistake. But since some advertisers are willing to pay more, we have been gradually increasing it, 10x at a time.