What is an SSP (supply-side platform)?

The publisher's side of programmatic

An SSP is the mirror of a DSP. Where the DSP decides what to buy, the SSP decides what to offer, to whom, and at what minimum price.

Practically, it takes a publisher's inventory, exposes it to exchanges and buyers, runs or participates in the auction, enforces floors and blocklists, and reports yield.

What it controls

• Floor prices, by placement, format and buyer — the primary yield lever.
• Demand source mix, including which exchanges see which inventory.
• Blocklists, both category and advertiser level.
• Deal management for private marketplaces and preferred deals.
• Signal enrichment — what context is passed to buyers, which materially affects clearing price.

SSP, exchange or network

These three are used interchangeably and are not the same. An ad network buys inventory and resells it, taking a position and a margin. An ad exchange is the auction venue and takes no position. An SSP is the publisher's own tooling for exposing inventory to those venues and managing terms.

The categories have blurred commercially — most large platforms perform more than one role — but the distinction still matters when you are working out whose incentive is whose.

The AI equivalent

An AI SSP does the same job for inventory that has no slots. Its distinctive work is deciding which conversations may carry advertising at all, and describing an eligible moment to buyers without sending them the conversation itself.

That second problem has no display analogue. A page can be named in a bid request; a private conversation cannot, so the platform must abstract it into a topic, an intent measure and a set of eligibility flags — and how well it does that largely determines what the inventory clears at.