Published: 17 September 2026

TL;DR: A DSP connects buyers to inventory through a bidding interface, charges a percentage of spend, and holds the buyer's record of what happened. Alkimi is a neutral agentic marketplace where buy-side and sell-side agents negotiate bilateral deals directly, with no percentage-of-spend fee and a shared DealSheet that both parties hold. The two serve different functions. A DSP handles open auction inventory. Alkimi handles bilateral deal negotiation with specific publishers where the buyer wants direct terms, a shared deal record, and a lower total technology cost.

The question of how Alkimi differs from a DSP comes up because both are technology platforms used in advertising transactions. The structural differences are specific and consequential, and they determine which platform is appropriate for which type of deal.

What a DSP Does

A demand-side platform connects buyers to advertising inventory through a bidding interface. When an impression becomes available on an SSP, the SSP sends a bid request to connected DSPs. The DSP evaluates the bid request against the campaign's targeting parameters, calculates a bid price, and submits a bid. If the bid wins, the impression is delivered.

The DSP charges a fee, typically expressed as a percentage of media spend. The buyer configures campaign settings in the DSP: targeting, bid caps, frequency caps, placement exclusions. The DSP holds the buyer's record of what happened: delivery data, spend data, performance data.

The DSP is an intermediary. It sits between the buyer and the inventory, manages the bidding process, and earns a fee on every transaction. The buyer's record and the publisher's record are separate. Post-campaign reporting compares the two.

What Alkimi Does

Alkimi is a neutral agentic marketplace. A buy-side agent operating under the buyer's mandate connects to a sell-side agent representing a specific publisher and negotiates a bilateral deal directly. The negotiation follows the AdCP protocol: proposal, counter-proposal, acceptance. No bidding. No auction. No intermediary managing the process.

When the agents agree terms, the agreed terms are written to a DealSheet: a bilateral record held by both parties simultaneously. The deal record is not held by Alkimi on behalf of the buyer. It is held in shared state by both the buyer and the publisher. Alkimi provides the infrastructure for the negotiation and the record. It does not hold the record exclusively.

Alkimi charges a fixed fee per deal, not a percentage of deal value. A deal at a £10 CPM and a deal at a £50 CPM generate the same Alkimi fee. Alkimi has no financial interest in whether the agreed CPM is higher or lower.

The Deal Record Difference

This is the most significant structural difference. In a DSP-based transaction, the buyer's DSP holds the buyer's record. The publisher's SSP holds the publisher's record. These are separate records. Post-campaign reconciliation means comparing them.

In an Alkimi transaction, the DealSheet is bilateral. Both parties hold the same record, written at agreement time. There is no reconciliation gap because there is no separate buyer record and publisher record to reconcile. There is one agreed record.

This matters for audit. A buyer who wants to verify what was agreed retrieves the DealSheet. The record is independent of the publisher's cooperation. A publisher who wants to verify the terms they agreed retrieves the same DealSheet. The record is independent of the buyer's cooperation.

In a DSP-based transaction, the buyer's record of what happened is the DSP's record. If the buyer has a dispute with the DSP, or if the DSP's record is incomplete, the buyer has no independent reference. The DSP holds the record.

The Fee Structure Difference

A DSP earns a percentage of media spend. This creates a structural alignment between the DSP's financial interest and transaction volume: more spend means more revenue. Whether individual deals are priced well for the buyer is not the DSP's primary concern.

Alkimi earns a fixed fee per deal. This creates a different structural alignment: the fee is the same regardless of deal value, which means Alkimi has no incentive to push deal prices higher. The neutral fee model is consistent with neutral marketplace positioning.

How a Buyer Uses Both

A sophisticated buying team is not choosing between a DSP and Alkimi. The two platforms serve different functions in a portfolio of inventory sources.

The DSP handles open auction inventory: display, video, and CTV inventory bought through real-time bidding, where price discovery through auction is appropriate and the bidding interface is the right tool. DSP configuration manages this inventory: targeting settings, bid caps, placement exclusions.

Alkimi handles bilateral deal negotiation: specific publishers, specific inventory, specific terms, where the buyer wants a direct CPM agreement, a shared deal record, and a lower total technology cost than a DSP percentage-of-spend fee implies. Mandate governance manages this inventory: documented parameters, a buy-side agent, and a decision log that records every agreement.

The question is not which platform to use. It is which platform is appropriate for which inventory type and deal structure. Open auction: DSP. Bilateral deals with specific publishers: Alkimi.