OpenX redraws the SSP-agency relationship
By Seb Joseph • December 3, 2025 •
Ivy Liu
Supply-side platforms (SSPs) were originally built as publisher advocates. Their job was straightforward: get impressions into the market and take a cut. Then they decided to work with advertisers, a move that never sat easily with the publishers who built their ads businesses on them.
The contradiction was obvious. An outfit meant to push prices up for sellers was now courting buyers trained to push them down.
SSPs brushed off the tension, arguing that better data and smarter buying would lead to higher publisher revenue. OpenX leaned into that pitch more than most, and the bet appears to be paying off.
Its agency-facing business has grown 200% over the past two years, said its president Matt Sattel.
Taken alone, the number lacks context. But it does underscore how a once powerful relationship between SSPs and agencies has shifted into something more direct – and far more commercially significant – than it used to be.
“From 2023 to 2025, we’ve grown our buyer sales team over 200%,” said Sattel. “That is ultimately because we believe that we have to service agencies and become a very buyer-driven organization in order to drive value to publishers.”
In practice, this means a few different things.
Over the last year, the ad tech vendor has been running sessions with every major holding company and a “many independents,” said Sattel, with execs walking those teams through supply-path diagnostic, s-chain analysis and directness scoring to help them understand where duplication, recycled inventory and made-for-arbitrage sits inside their buying. These meetings aren’t surface-level roadshows, continued Sattel. Agency execs are shown log-level discrepancies between SSPs and walked through how inflated queries-per-second scores manifest inside demand-side platforms – the kind of education that traditionally came from consultants rather than supply partners.
“Buyers are saying we really need to have strong relationships with our SSPs and we need to be selecting them based on those who are making responsible decisions rather than the ones that are inflated because of bad practice,” said Sattel.
OpenX’s product footprint has followed suit.
It has rebuilt its curation platform with direct input from agencies, moving from a behind the scenes utility for data vendors into a tool buyers can use directly to assemble, tune and audit their own supply packages. Agencies can filter inventory by provenance, directness to publisher and content-level CTV signals, and see how those variables change the underlying supply graph before anything goes live.
That level of visibility isn’t something SSPs usually hand over. They were never structured or incentivized to offer that kind of transparency. Their mandate has been to maximize publisher yield, while curators have always optimized supply to buyer criteria. Only recently have those two aims started to overlap.
“We’ve had our curation platform in market since 2018 but we recently decided that this was going to be something we put in the hands of buyers,” said Sattel. “It was a way for data providers like Audigent or Samba to actually utilize our curation platform to get deals to DSPs on behalf of buyers.”
What those buyers ultimately want is predictability. Which is why OpenX removed MFA from its marketplace, avoided request duplication to game DSP algorithms and built controls to prevent resold impressions from entering its marketplace. Those choices, according to Sattel, run counter to the growth tactics many competitors rely on but are the foundation for the “clean supply” agencies increasingly track when deciding which ones to spend their money with.
“We process about 500 billion impressions daily, whereas our competitors are between 850 billion to a trillion,” said Sattel. “Marketers are increasingly aware that we all have access to the same amount of direct supply and are subsequently trying to understand that discrepancy.”
Much of what Sattel has described will sound familiar to anyone who lived through the first wave of supply-path optimization. SSPs and agencies cast themselves as partners on opposite sides of the market, aligned around buyers’ clearer views of what they were paying for. Some of that happened. Often, commercial incentives shaped the relationship more than the pitch.
The balance has since steadied. It’s still far from seamless but SSPs say the conversations now center on helping advertisers make sharper, more informed decisions, not just on the deal mechanics that defined the earlier era.
“Buyers are no longer thinking of SSPs as just pipes,” said Sattel. “They’re thinking about them as a way to make their programmatic media buys smarter and better, and in many situations more efficient and able to drive better performance.”
That came through loud and clear at Digiday’s Programmatic Marketing Summit in New Orleans this week. According to the agency execs who attended, those vendors are becoming more crucial to how they sort the wheat from the chaff when it comes to ad inventory.
“I think the opportunity with SSPs is going to evolve when it comes to the different revenue streams, more transparency and just opportunity,” said Hillary Kupferberg, vp of performance marketing at Exverus by Brainlabs.
How quickly the shift plays out now hinges on SSPs. Agencies say they’re ready to cut deeper, more structured deals – at least the ones at the summit. But that’s predicated on SSPs being transparent about what those deals actually cost and what agencies are buying.
Too much money is at stake for agencies to move forward without knowing what sits inside the pipes.
