Supply path optimization (SPO) means steering spend toward shorter or preferred routes to the same inventory. IAB Tech Lab described it that way in 2019, as one use of sellers.json and the SupplyChain object. A shorter path has fewer parties for a buyer to verify. The evidence for a path comes from public files and the bid request, not from guesswork.

How does the Tech Lab define SPO?

The Tech Lab’s 2019 adoption post lists four impression-level decisions that sellers.json and the SupplyChain object make possible:

  • Validate the complete financial path against ads.txt entries.
  • Block impressions that travel through untrustworthy intermediaries, judged by outside data.
  • Block impressions that pass through more than n intermediaries, where the buyer or platform picks n.
  • Prioritize spend through shorter or preferred paths over longer or less preferred ones. That fourth decision is SPO.

The post gives a lack of TAG certification and a poor previous experience as examples of the outside data behind the second decision. So SPO sits inside a wider set of path checks, and the first of them is validation.

What evidence does a DSP use to find a shorter path?

Three signals do most of the work.

  • DIRECT or RESELLER in ads.txt. A DIRECT record means the publisher controls the account, according to the ads.txt 1.1 spec.
  • MANAGERDOMAIN. The same spec says this variable should point to the most direct path to purchase when a publisher outsources monetization. The implementation guidance says buyers asked to minimize the number of hops, and that for a publisher who outsources most monetization, the most direct route may run through a reseller.
  • The schain node list. Its length shows how many parties handled the request, and each node can be checked against the files.

What do the ANA studies say about concentration?

Two ANA releases frame the cost of sprawl. Their scopes differ, so read them separately.

The ANA’s 2023 study, released June 19, 2023, covered $123 million of ad spend and 35.5 billion impressions from 21 member companies between September 2022 and January 2023. It reported that the average campaign ran on 44,000 websites, and said advertisers can reach a high percentage of target audiences with a few hundred. It also found that made-for-advertising sites made up 21 percent of impressions and 15 percent of spend. The report said advertisers often chase cheap CPMs, and that cheap inventory is not always quality inventory. The ANA added a caution: cutting sites should not disadvantage small or minority-owned providers.

The ANA’s Q1 2026 benchmark, released May 27, 2026, is quarterly and impression-level. It found that higher-performing advertisers converted 54.0 percent of programmatic spend into qualified impressions, against 32.1 percent for lower performers. The release says higher performers operated with significantly more concentrated supply footprints. It lists that beside better measurement coverage and higher viewability, so it does not isolate concentration as the cause. The release also says the gap is driven far more by media productivity than by transaction costs. Its market-level TrueAdSpend Index, the share of programmatic spend delivering fraud-free, measurable, viewable and MFA-free impressions, rebounded to 43.3 percent in Q1 2026. Participating marketers rose from 54 to 86 in Q1 2026, so the benchmark’s base changed in the quarter it reports.

Is a shorter path always better?

Not by itself. The path is one input beside quality and cost, and the ANA 2026 release calls quality, not cost, the main differentiator.

Node counting is also getting harder to read. The Tech Lab’s SupplyChain v1.1 announcement says chains will become longer as transparency improves, while expecting the update to help buyers with SPO and cut duplicate bid requests. A longer chain that discloses every party can tell a buyer more than a short chain that hides some. The v1.1 text is still a draft as of October 2, 2026.

How does Vectravia handle this?

Path Check applies supply path optimization to authorized paths, preferring the shorter ones. For each placement it shows whether the relationship is DIRECT or RESELLER. It also supports made-for-advertising and pirate-domain exclusion lists.