Open Auction (Open Marketplace)
An open auction, also called the open marketplace, is the most public form of programmatic buying, where inventory is offered to all eligible buyers via RTB with no pre-negotiated deal, and the highest bidder wins.
Key takeaways
- The open auction offers inventory to all buyers with no prior agreement.
- It maximizes reach and competition but offers the least control over quality and pricing.
- It sits at one end of a spectrum that runs through PMPs to programmatic guaranteed.
- Supply-path optimization and sellers.json exist largely to police open-auction quality.
Where the open auction fits
Programmatic deal types form a spectrum. The open auction is the most liquid and least controlled: maximum reach, real-time price discovery, but exposure to lower-quality or misrepresented inventory. Private marketplaces add invited buyers and floor prices; programmatic guaranteed removes the auction entirely with a fixed price and volume.
Quality and transparency tools
Because the open auction is where fraud and misrepresentation concentrate, the industry layered on safeguards: ads.txt / app-ads.txt to authorize sellers, sellers.json and the supply chain object to expose the resale path, and supply-path optimization on the buy side to prune redundant routes.
| Access | Open to all eligible buyers |
|---|---|
| Control | Lowest of the programmatic deal types |
| Reach | Highest / most liquid |
| Guardrails | ads.txt, sellers.json, SupplyChain object, SPO |
Frequently asked questions
What is the difference between the open auction and a PMP?
The open auction is available to all buyers with no agreement; a private marketplace is an invitation-only auction with negotiated floors and, often, better inventory transparency.
Is open-auction inventory lower quality?
Not inherently, but it carries the most risk of fraud and misrepresentation, which is why authorization standards like ads.txt and sellers.json matter most there.