What is OpenRTB?

Also known as: OpenRTB 2.6, Real-Time Bidding protocol

Quick definition

OpenRTB is the IAB Tech Lab specification that standardizes how an exchange or SSP sends a bid request describing an impression to DSPs and how DSPs answer with a bid response, so thousands of buyers and sellers can trade in real time through one common JSON message format.

How it works

User opens a page or app; an ad slot becomes available
SSP/exchange builds a bid request (imp, site/app, device, user, regs objects)
Request fans out to DSPs, usually with a ~100–300 ms timeout
DSPs return bid responses with price, creative markup and deal ID
Exchange runs the auction and fires win / billing / loss notices

Key points

Steward: IAB Tech Lab. 2.x is the version deployed at scale; 2.6 added CTV pod bidding, richer supply chain and loss-reason signals.
Core objects: BidRequest → Imp (banner/video/audio/native) → Site or App → Device → User → Regs; response is BidResponse → SeatBid → Bid.
Extensions: Vendors use the ext object for non-standard fields, which is where most integration drift happens.

Benefits

One integration pattern reaches many partners
Supports deals, floors and supply-chain transparency (schain)

Trade-offs

Heavy use of ext fields fragments implementations
Version adoption lags; many endpoints still run partial 2.5

FAQ

What is the difference between OpenRTB 2.6 and 3.0?

2.6 is an incremental update of the widely deployed 2.x line. 3.0 restructured the model into layers (transport, OpenRTB, AdCOM), but saw limited adoption, so most of the market extended 2.x instead.

Who uses OpenRTB?

SSPs, ad exchanges, DSPs, ad networks and header bidding wrappers use it to exchange bid requests and responses.

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Official sources

IAB Tech Lab – OpenRTB

Last reviewed 2026-10-27. Explanations are written by AdTech Radar; consult the official specification for implementation.

Related terms

Header Bidding

Header bidding is a technique where a publisher offers each impression to multiple SSPs and exchanges simultaneously before calling its ad server, so demand competes on price at once instead of in a sequential waterfall.

sellers.json & SupplyChain Object

sellers.json is a file published by an SSP or exchange that discloses the identity of each seller account it represents, while the SupplyChain object in the bid request records every hop the impression passed through; together with ads.txt they let buyers verify the full path from publisher to DSP.

Supply Path Optimization (SPO)

Supply path optimization is the practice of buyers choosing the fewest, cheapest and most transparent routes to the same publisher inventory, cutting redundant resellers so more of the media budget reaches the publisher.

Bid Shading

Bid shading is a DSP algorithm that lowers a bid below the buyer's maximum value in first-price auctions, estimating the lowest price likely to still win so advertisers do not overpay.