Real-Time Bidding (RTB)

Real-time bidding (RTB) is the automated auction that sells an ad impression while the page or app is loading, usually through the OpenRTB protocol. In retail media, RTB carries offsite and programmatic display buys. Onsite sponsored-product auctions run inside the retailer’s own platform, and an OpenRTB extension for them arrived in 2025.

Learn more

By Mateusz Drela, CEO of RMIQUpdated · 5 min read

How real-time bidding works

Take a brand that buys a retailer's shopper audience offsite through a demand-side platform, as Amazon DSP lets advertisers do with audiences based on Amazon's first-party buying signals across third-party apps, sites and devices. OpenRTB defines RTB as bidding for individual impressions in real time, while a consumer is waiting. Each impression passes through platforms on both sides in five steps:

  1. A shopper opens a publisher's page or app with an ad slot. The publisher's ad server passes the opportunity to a supply-side platform (SSP), which sends it to an ad exchange.
  2. The exchange sends a bid request describing the impression to bidders, including the brand's demand-side platform (DSP).
  3. The DSP values the impression against what it knows about the user and the campaign's audience, then answers within the request's time limit, set in milliseconds, with a bid response or an empty no-bid.
  4. The exchange picks a winner under the auction rules in force. The request's auction type field says whether that is first price or second price plus.
  5. The exchange can send win, billing and loss notices, and the winning ad is served.

Kevel's documentation notes that although the process has several steps, it takes milliseconds. An onsite sponsored-product auction usually works without steps 2 and 3, because the advertisers' bids already sit in the retailer's system, as the next section explains. The first-price auction and floor price entries cover how the winning price is set.

Real-time bidding in retail media: offsite and onsite

Offsite, RTB works much as it does on the open web, as in the Amazon DSP case above. Kroger's Private Marketplace, announced in 2021, was built to let brands apply Kroger audience data to programmatic campaigns in the DSP of their choice, and Grocery Dive reported that its deal ID was meant to protect consumer privacy. In OpenRTB, a deal is a pre-arranged agreement between a publisher and a buyer's seat, and an impression can be subject to a private marketplace. The onsite vs offsite advertising entry explains the two channels.

Onsite sponsored products follow a different flow. These auctions also run in real time, inside the retailer's own platform, on bids that advertisers set in advance. When a customer searches Walmart's site or app, Walmart's platform runs a real-time auction and awards the placement to the most relevant ad. Amazon says it reviews billions of bids a day and ranks ads on relevance and bid, with each advertiser bidding a maximum price for a placement. Sponsored product ads also need creatives built from the retailer's product feed, and according to Pentaleap, slow load times long kept RTB out of onsite sponsored products.

Example: real-time bidding for sponsored products

In January 2025, after a public comment period that began in December 2024, IAB Tech Lab finalized an OpenRTB extension that brings onsite product listing ads into the bid request. On July 24, 2025, Pentaleap and Teads announced an RTB integration for retailers' onsite Sponsored Product Ads. The companies say it lets advertisers activate Sponsored Product inventory across multiple retail networks through one platform, Teads Ad Manager, and they describe it as an industry first. They add that retail media can then be managed alongside display, video and CTV campaigns in a single line item.

IAB Tech Lab framed the shift as early. In January 2025 it said commerce media lacked implementation of some of the most fundamental industry standards, and it called the product listing release the first step of many.

Why it matters for brands and sellers

Onsite and offsite buys run on different mechanics, so plan them separately. Onsite, you set cost-per-click bids per keyword in the retailer's console, and its auction weighs relevance alongside your bid. Offsite, a DSP bids on each impression it is offered, within a time limit measured in milliseconds. The auction-based pricing entry covers how the onsite price is set.

One route for retailer data into offsite buys is a deal, as in Kroger's marketplace above, and the bid request entry shows how deals and audience segments travel. A bid request can also carry privacy signals, including a GDPR flag and US Privacy and Global Privacy Platform strings, which tell bidders which rules govern the data. Before planning an offsite campaign, check which deals and audiences a network sells. The retail media networks hub, the Amazon Ads guide and the Kroger retail media network profile are useful starting points.

Frequently asked questions

What is real-time bidding in advertising?

Real-time bidding (RTB) is an automated auction that sells individual ad impressions as they occur, while the viewer waits for the page or app to load. IAB Tech Lab describes it as an on-the-spot programmatic auction, similar to how financial markets operate. In retail media it powers offsite programmatic buys.

What is the difference between RTB and programmatic advertising?

Programmatic advertising is the wider category of automated ad buying, and RTB is one type of it. Amazon Ads lists private marketplaces and programmatic direct as other types, which give publishers different controls over how they sell inventory. In OpenRTB, private marketplace deals still travel in the bid request, attached to the impression.

Do Amazon and Walmart sponsored product ads use real-time bidding?

Their sponsored product auctions run in real time inside each retailer's own platform, on bids that advertisers set in advance. Walmart's platform runs a real-time auction when a customer searches, and Amazon says it ranks ads on relevance and bid. In January 2025 IAB Tech Lab finalized an OpenRTB extension for buying onsite product listing ads programmatically.

Does real-time bidding raise privacy concerns?

It does. RTB depends on collecting and sharing data about users and their activities, and it has attracted attention from data protection authorities. OpenRTB lets a bid request carry a GDPR flag, a US Privacy string and a Global Privacy Platform string, so bidders know which rules apply.

How RMIQ can help you with RTB

RMIQ accelerates real-time bidding (RTB) performance by unifying planning, activation, and optimization across Walmart, Instacart, Amazon, Sprouts, Thrive Market, Target, Uber, and more than twenty additional retail media networks, eliminating fragmented dashboards and manual data wrangling while enabling brands to execute precision strategies from a single pane of glass. Its multi-agent AI architecture deploys specialized autonomous agents for bid adjustment, budget allocation, cross-network learning, A/B testing orchestration, and strategy refinement that continuously learn in real time to maximize ROAS, routinely delivering average gains exceeding 50% and as much as five dollars in incremental sales for every dollar invested, all without constant human intervention.

By pairing broad network coverage that reaches up to 85% of the U.S. retail audience with SKU-level insights, granular keyword optimization, and adaptive pacing, the platform identifies high-intent shoppers, aligns bids to true marginal value, and reallocates spend to outperform market volatility during auctions. The result is faster, smarter RTB that scales from emerging brands to global enterprises managing thousands of SKUs, supported by rapid onboarding—often in under five minutes—and white-glove customer success. Moreover, RMIQ’s consolidated reporting, alerting, and workflow automation streamline governance, giving finance, sales, and media teams shared visibility into spend, performance, and forecasted outcomes while reducing operational overhead.

With real-time experimentation, creative rotation, and inventory-aware rules, the system protects efficiency during supply fluctuations and seasonality, auto-pausing underperformers and amplifying winning combinations across networks. Built for auditability, it preserves decision logs and learning artifacts for compliance and post-campaign analysis, ensuring repeatability and continuous improvement. In short, RMIQ modernizes RTB by combining expansive reach, autonomous optimization, and practical usability, helping B2B marketers capture demand, defend share, and compound returns in an increasingly competitive retail media ecosystem. It integrates with existing analytics, honors brand guardrails, supports granular permissions, and offers SLAs aligned to enterprise procurement standards requirements.

Our Current Partners

We are already helping leading retailers and platforms grow their retail media businesses, including:

Become a partner

Drop your email 

and we’ll show you how to double your retail media ROAS – no strings attached