TL;DR: Supply path optimisation (SPO) is the process by which buyers reduce the number of intermediary hops between their budget and the publisher's inventory, with the goal of increasing the proportion of media spend that reaches the publisher and improving transparency over what was bought. Conventional SPO focuses on reducing SSP redundancy within the existing programmatic structure. Agent-to-agent bilateral negotiation offers a more direct form of SPO by removing intermediary layers entirely for qualifying inventory.

Supply path optimisation became a buyer priority after the industry began to understand how much of a programmatic budget was absorbed by intermediary fees before reaching the publisher. ANA's 2023 programmatic transparency study documented this at scale: a substantial portion of programmatic spend was being lost to intermediaries, with publishers receiving significantly less than the gross spend the buyer believed they were committing to a given publisher relationship.

The conventional response was SPO: reducing the number of SSP paths through which a given publisher's inventory was accessed, preferring the path with the fewest hops and the most transparent fee structure. This was a meaningful improvement, but it operated within the existing programmatic architecture rather than replacing it.

What conventional SPO involves

Conventional SPO has three components.

Preferred path selection. For a given publisher, the buyer identifies which SSP paths provide the most direct route to the publisher's inventory and the most transparent fee structure. The buyer then configures their DSP to preference these paths over others when bidding on that publisher's inventory.

SSP consolidation. Rather than bidding through all available SSPs for a given publisher, the buyer reduces to a shorter list of preferred SSPs. This reduces duplication, where the buyer was effectively competing against themselves across multiple bid streams for the same impression.

Fee auditing. The buyer audits the total technology fee for a given supply path: DSP fee plus SSP fee plus any data or verification fees. The goal is to understand the total cost of reaching the publisher's inventory, not just the CPM paid.

Conventional SPO reduces intermediary costs, but it does not eliminate them. There is still a DSP between the buyer and the publisher, and there is still at least one SSP. The fee stack is reduced, but it remains a stack.

What agent-to-agent bilateral negotiation adds

Bilateral agent-to-agent negotiation offers a more direct form of SPO for qualifying inventory. Instead of routing through a DSP and an SSP to reach the publisher's inventory, the buyer's agent negotiates directly with the publisher's sell-side agent through a neutral marketplace that charges a fixed deal fee rather than a percentage of transaction value.

The supply path in this model has two parties (buyer and publisher) and one marketplace. The DSP layer is replaced by the mandate that the buyer's agent operates under. The SSP layer is replaced by the publisher's sell-side agent and the marketplace's deal record infrastructure.

This is a more complete form of SPO for the inventory it covers. It does not apply to all inventory: open auction inventory that the buyer acquires at scale and where price discovery through auction is the right mechanism does not benefit from bilateral negotiation. But for premium publisher relationships where the buyer is spending significantly and where the publisher has a clear price floor, bilateral negotiation provides a supply path that is shorter and cheaper than anything conventional SPO can achieve within the auction framework.

How buyers use both approaches together

In practice, buyers pursuing supply path efficiency use conventional SPO and bilateral negotiation for different parts of their inventory mix. The two approaches are not in competition; they address different buying scenarios.

Conventional SPO applies to all open auction spend. Reducing SSP redundancy and preferring lower-fee paths is relevant for any inventory the buyer acquires through the auction. This is the baseline.

Bilateral negotiation applies to the highest-value publisher relationships where the inventory is worth the mandate investment and where the publisher has the infrastructure to support agent-negotiated deals. This is an incremental layer on top of the conventional SPO baseline.

The total supply path efficiency improvement is the combination of both: conventional SPO applied to the open auction portion of spend, and bilateral negotiation applied to the direct publisher portion.

What SPO outcomes buyers should expect to measure

Supply path efficiency improvements are measured in two ways.

Net publisher revenue percentage. The proportion of gross media spend that reaches the publisher as net revenue. Conventional SPO typically improves this by reducing SSP fee redundancy. Bilateral negotiation improves it further by replacing percentage-of-spend fee structures with fixed deal fees.

Deal record quality. Bilateral negotiation produces a DealSheet that both parties hold. Post-campaign reconciliation against a shared deal record is more efficient and less dispute-prone than reconciling two separate logs from a DSP and an SSP. This is a governance benefit, not a direct cost reduction, but it reduces the operational cost of post-campaign reconciliation.

Buyers should establish a baseline for both metrics before implementing SPO changes, so the improvement is measurable rather than assumed.