Last updated: 13 October 2026

Supply path optimisation (SPO) is the practice of choosing the most direct, transparent and cost-efficient route from an advertiser's budget to a publisher's inventory, and cutting the routes that add fees without adding value. It is supported across the programmatic stack: demand-side platforms let buyers prefer and prune paths, supply-side platforms and curators offer shorter routes, verification vendors score path quality, and IAB Tech Lab's ads.txt, sellers.json and SupplyChain object make each path inspectable.

TL;DR. Supply path optimisation reduces the intermediaries between buyer and publisher to improve fee efficiency, transparency and inventory quality. It is done today with ads.txt, sellers.json and the SupplyChain object, plus path pruning, SSP consolidation, fee auditing and curated deals. DSPs, SSPs, curation platforms and verification vendors each support SPO at a different point in the path. AI turns SPO from a periodic review into a continuous decision, and agent-to-agent negotiation can shorten the path to a buyer, a seller and a marketplace. What does not change is the dependence on data the buyer can verify.

What is supply path optimisation?

Supply path optimisation is a buyer-side discipline that asks, for each step between advertiser and publisher, whether that step adds value proportionate to its cost and its opacity. One publisher's impression may be offered through many supply-side platforms (SSPs), exchanges and resellers at once, and some of those paths add fees, latency or doubt about who is really selling. SPO favours the direct, cheaper and verifiable paths and drops the rest.

SPO targets three outcomes: more of each pound reaching the publisher, visibility of where the money goes, and confidence that the inventory bought is what the seller claims. Done well, SPO is governance. Done badly, it moves fees around without shortening the path.

Why does supply path optimisation exist?

Supply path optimisation exists because the programmatic supply chain grew by accretion and leaks value at a scale the industry has measured. The ISBA and PwC Programmatic Supply Chain Transparency Study, published in May 2020, found that publishers received 51% of UK advertiser spend, and that around 15% of spend was an "unknown delta" that could not be attributed to any party. A follow-up study published in January 2023 found the share of impressions matched from advertiser to publisher had risen to 58%, from 12%, and the unknown delta had fallen to 3%. That follow-up covered the premium end of the market only.

How is supply path optimisation done today?

Supply path optimisation combines transparency standards, which make each path visible, with buyer decisions about which paths to keep.

The standards come from IAB Tech Lab. ads.txt, introduced in 2017, is a file on the publisher's domain listing the companies authorised to sell its inventory, directly or as resellers. sellers.json, introduced in 2019, is the mirror image: each SSP or exchange lists the sellers it represents and whether each is a publisher or an intermediary. The SupplyChain object (schain), an IAB Tech Lab extension to OpenRTB, travels inside the bid request and lists every entity that handled it. Read together, the three let a buyer count the hops on a path and check that each hop is authorised.

Buyers act on that visibility in four ways. Path pruning sets the DSP to prefer the most direct authorised route to each publisher and ignore reseller routes that duplicate it. SSP consolidation shortens the list of active SSPs, which also stops the buyer bidding against itself for one impression across several bid streams. Fee auditing totals the DSP, SSP, data and verification fees on each path, not just the CPM. Curation packages chosen publishers and routes into a deal, so the short path is the default rather than a setting someone maintains.

Which platforms support supply path optimisation?

Supply path optimisation is not a single product. Support is spread across the stack.

Demand-side platforms (DSPs) are where most SPO decisions execute: buyers set preferred paths, exclude resellers and read the SupplyChain object at bid time. Some DSPs also connect directly to publishers to remove the SSP hop; The Trade Desk's OpenPath is the best-known example.

Supply-side platforms (SSPs) publish sellers.json, pass complete SupplyChain objects and offer direct routes to buyers who consolidate spend with them.

Curation platforms package publishers, audiences and routes into deals that buyers activate in their DSP.

Verification vendors, such as Integral Ad Science and DoubleVerify, measure invalid traffic, viewability and brand safety. Reported by path, they show which routes deliver what they claim.

Agentic marketplaces are the newest category: buyer and seller agents negotiate deal terms directly through a marketplace rather than a DSP and SSP chain.

How does AI change supply path optimisation?

AI does not change what supply path optimisation is for. It changes how often and how finely it runs.

Human SPO runs as a periodic review: a team cuts wasteful paths and revisits the list months later. An AI system evaluates paths continuously, so a route that starts adding fees or serving worse inventory is dropped as it degrades. It can also weigh each path against the goal of a specific campaign rather than one standing rule. Treating the path as one lever alongside targeting and bidding, it can also spot a segment that underperforms because of its path rather than its audience.

How does agent-to-agent negotiation change the supply path?

Agent-to-agent negotiation changes the shape of the supply path, not only the choice between existing paths. A buyer's agent negotiates terms directly with a publisher's seller agent, usually through a marketplace, so the path becomes buyer, seller and marketplace. The buyer's mandate takes over much of the DSP's decision role, and the seller agent much of the SSP's.

This suits some inventory, not all. Open auction inventory, where the auction is the right way to discover price, stays in the conventional stack. Direct negotiation suits premium publisher relationships with meaningful spend and a clear price floor. Conventional SPO remains the baseline for auction spend, with agent negotiation as a layer on top for selected publishers.

IAB Tech Lab announced AAMP, its Agentic Advertising Management Protocols, in early 2026. AAMP extends existing standards rather than replacing them; according to IAB Tech Lab, its Deals API support covers programmatic guaranteed, preferred deals, private marketplaces and the open marketplace. AdCP, the Ad Context Protocol published separately by AgenticAdvertising.org, lets publishers declare which agents may sell their inventory in an adagents.json file on their own domain, an idea that echoes ads.txt.

Does a shorter supply path make verification easier?

A shorter supply path does not automatically make verification easier. The programmatic chain does verification work: SSPs vet publishers, DSPs filter quality and third-party vendors check viewability and brand safety. When agents negotiate directly, those checks do not transfer by default, and the buyer's agent must test each seller's claims itself.

The answer is to build verification into the deal. A deal that states the inventory, audience, delivery conditions and remedies for shortfall can be checked afterwards against a shared record. Intermediaries that only connect buyers to sellers lose ground in that model; intermediaries that verify gain it.

What does not change in supply path optimisation?

The problem does not change. The fees, unattributed spend and low-quality inventory that SPO exists to cut are structural, and an agent does not remove them by being fast.

The dependence on data does not change. SPO has always been limited by what the buyer can see. Where path data is thin, an agent optimises in the dark, faster than a human would.

What changes is the cost of opacity. A person doing SPO badly does it slowly; an agent on unreliable data does it continuously and at scale, so opacity now spoils the decision during the campaign, not just the report after it. When agents on both sides of a deal each keep their own log, even the record of what a path delivered can be disputed. Alkimi, an agentic advertising marketplace, addresses that with a DealSheet, a shared deal record that both buyer and seller hold, with humans keeping approval rights at the deal level.

Frequently asked questions

What is the difference between ads.txt and sellers.json?

ads.txt is published by the publisher and lists who is authorised to sell its inventory. sellers.json is published by the SSP or exchange and lists the sellers it represents.

What is the SupplyChain object?

The SupplyChain object, or schain, is an IAB Tech Lab extension to OpenRTB that lists every entity that handled a bid request, so buyers can count hops and spot unauthorised resellers.

Is supply path optimisation the same as cutting SSPs?

No. SSP consolidation is one SPO tactic. SPO also covers fee auditing, path pruning, curated deals and direct agent-to-agent negotiation with selected publishers.

Does supply path optimisation still matter when AI agents do the buying?

Yes, more than before. An agent acts on whatever path data it receives, so unreliable data distorts live decisions rather than only the post-campaign report.

How should a buyer measure whether SPO is working?

Track the share of gross media spend that reaches the publisher as net revenue, and the quality of the deal record used for reconciliation. Set a baseline for both before changing paths.

What Is Supply Path Optimisation and Which Platforms Support It?