Here is a story we have seen too many times. An advertiser opens a popunder campaign for India, sees the recommended bid, decides to be safe and puts $2.00 CPM. India popunder traffic clears at about $0.30. The campaign wins almost everything it enters, the $60 test budget buys 30,000 impressions, nothing converts at that sample size, and the advertiser leaves with the conclusion that “pops don’t work for us”.
At the market price the same $60 would have bought three to ten times more impressions. Not because the traffic was different, but because the advertiser paid for a margin of safety that the auction never asked for.
Smart CPM removes that margin. Your bid becomes a ceiling. What you are charged is the price the traffic actually clears at, per source and per geo.
What changes
Nothing in the campaign form. You still set a CPM bid on a popunder campaign. What changes is how the impression is priced after you win it:
- The auction ranks you by your full bid. Priority against other advertisers is unchanged. Smart CPM never makes you lose an auction you would have won.
- The charge is the lower of your bid and the market price for that source and geo. If the market price is above your bid, you pay your bid, exactly as before.
- The saving stays in your budget. Same daily budget, more impressions, lower effective CPM.
The auction outcome is decided first, the price second. That order is what keeps Smart CPM from changing who wins.
Where the market price comes from
Adexium buys popunder inventory from many supply partners, and each partner runs a first-price auction: the price we quote is the price we pay. There is no second-price discount to pass along. So the only way to know what a source really costs is to measure our own win rate at every price we have quoted.
That is what we now do. For every pair of traffic source and country, the bidder keeps a curve of win rate against price, built from the last seven days of real quotes and real wins, refreshed every 30 minutes. The market price for the pair is the knee of that curve: the lowest price that still delivers at least 95% of the best win rate we have observed. Above the knee, more money buys almost no additional traffic. That is where your charge is set.
A pair only gets a market price when there is enough data behind it: at least ten thousand quotes, several distinct price levels, and a curve that flattens inside the observed range. A pair that keeps climbing to the edge of what we have measured is left alone, because a knee we cannot see is not a knee. Where a pair has no valid price, you pay your bid, as before.
A small share of impressions on every pair, about one in twenty, is always charged at the full bid. That is not a fee: it is how we keep observing the expensive end of the curve. If the market moves up, the next refresh sees it and the charge follows within half an hour instead of drifting for a week.
What we measured before switching it on
We ran Smart CPM in shadow mode first: the bidder calculated what it would have charged and wrote it down next to what it actually charged, without changing anything.
On the popunder sources with a valid market price, 12.3% of won impressions would have been charged less, by $1.35 CPM on average. That average is the size of the safety margin advertisers put on top of the market without knowing it. On one Thailand popunder source the price that kept the same win rate was $0.41 instead of the $1.00 advertisers were paying.
We also caught, in shadow, a bug that would have silently skipped every internal campaign. Shadow mode exists for exactly that reason. It was fixed before Smart CPM touched a single charge.
What you will see in your stats
Your bid stays what you typed. Your eCPM, spend per 1,000 impressions in Analytics, drops below it on sources where the market is cheaper. Impressions per dollar go up. Win rate and the Delivery page stay the same, because the auction is unchanged.
If you have been using bid as a proxy for “how much am I paying”, switch to eCPM. From now on those are different numbers by design.
Scope and rollout
Smart CPM applies to fixed-bid CPM campaigns on popunder inventory. It went live on September 8 on the supply partner where shadow data showed the biggest gap between bids and clearing prices, and after a clean first day it was extended to every popunder source. A source is priced at market as soon as it accumulates enough quotes for a trustworthy curve; until then you pay your bid. You do not need to change anything in your campaigns.
Not covered, and why:
- Auto CPA campaigns. They already compute their own per-source price from your target; putting a second pricing layer under them would fight the first. Pick one: Auto CPA when you have conversions to optimize on, fixed bid with Smart CPM when you buy on CPM.
- Push and CPC campaigns. CPC prices on push cluster around a handful of values, so there is no natural spread to build a curve from. Pricing push at market would need deliberate price experiments on live traffic, which is a separate decision we have not made.
- CPA-billed campaigns. There is no CPM to shade.
Why we give the saving back instead of keeping it
A network that pays sources the market price and charges advertisers their full bid earns more per impression. We chose the other design. An advertiser with a fixed budget spends the same amount either way; the difference is whether that budget buys 30,000 impressions or 100,000, and whether the test finds its conversion or not. Advertisers who find their conversion stay. That is worth more to us than the margin on a test that fails.
Set your ceiling honestly, and let the price find the market. Create a popunder campaign or open an existing one; nothing else is required.
