Glossary
SPO (supply path optimization)
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Supply path optimization is the practice, by a buyer or DSP, of choosing which of the many available routes to the same publisher impression to bid through, based on fees, auction rules, latency and transparency, and cutting off the others.
The same impression often reaches a DSP through several SSPs and resellers, each with its own fee and auction behavior. SPO means bidding only through the paths that return the most media for the money, usually the publisher's direct SSP integrations. The evidence that paths differ is strong: Adalytics found one SSP charging a single publisher between 7% and 42% on the same site with the same buyer and DSP (ExchangeWire, 16 September 2026). The tools for SPO are the transparency files: ads.txt tells the buyer which sellers are authorized and whether each is DIRECT or RESELLER, sellers.json tells it who each seller ID is, and the SupplyChain object in each request shows the full path (IAB Tech Lab, Supply Chain and Foundations).
SPO is also a QPS strategy. Fewer paths means fewer duplicate requests for the same impression, which is what Amazon Ads' Dynamic Traffic Engine, donated to IAB Tech Lab on 15 April 2026, formalises as a file that DSPs publish and SSPs poll (IAB Tech Lab, 15 April 2026).
Example: a DSP sees the same news-site impression via SSP A (DIRECT, schain of one node) and via reseller B (RESELLER, schain of three nodes, 15 points higher fee); it bids only through A.
Related: DPO, SupplyChain object, ads.txt, sellers.json, QPS.
Source: IAB Tech Lab, Supply Chain and Foundations pillar (ads.txt, sellers.json, SupplyChain); ANA and Adalytics findings via ExchangeWire (16 September 2026).