Retail Media Interoperability: Beyond the Walled Garden

Retail Media was built on a powerful idea: connecting advertising and commerce within the same environment. Retailers could combine customer data, media inventory and transactions, giving advertisers something traditional digital advertising struggled to offer: a direct connection between media exposure and sales.

That model helped turn Retail Media into one of the fastest-growing areas of advertising. However, its success is creating a new challenge. Brands increasingly operate across multiple Retail Media Networks (RMNs), each with its own audiences, activation capabilities and measurement methodologies.

The result is a new paradox: the closed ecosystems that made Retail Media valuable can also make it increasingly difficult to scale.

The next phase of the industry may therefore depend on Retail Media interoperability. However, this does not mean eliminating walled gardens or making retailer data open. Instead, the challenge is to make retail data more useful across the advertising ecosystem without losing control over it.

Retail Media was built on exclusivity. Its next phase may depend on interoperability.

Retail Media Was Built as a Closed Loop

The first generation of Retail Media Networks had a structural advantage over traditional digital advertising. Retailers already knew what customers searched for, viewed and purchased. At the same time, they controlled many of the environments where those interactions happened.

This created a powerful closed loop: Customer Data → Media Activation → Transaction → Measurement. Advertising could sit close to the transaction, while commerce data supported targeting, optimisation and measurement.

For advertisers, this provided a clearer connection between media investment and sales. For retailers, it created a new revenue stream while protecting one of their most valuable assets: first-party commerce data.

The walled garden was therefore not a limitation of the original Retail Media model. It was one of its strengths. The problem emerged as the model scaled.

Growth Is Creating a Fragmentation Problem

Retail Media continues to expand rapidly. In the United States, digital Retail Media advertising is expected to reach approximately $69 billion in 2026. Europe is smaller but following a similar growth trajectory, with Retail Media already accounting for a significant share of digital advertising investment.

However, market growth also means more networks, platforms and measurement environments for advertisers to manage. A large brand may work with Amazon, Walmart and several national retailers while also investing across search, social media, connected TV and programmatic advertising.

Each network can provide valuable audiences and closed-loop measurement, but those capabilities often remain separated. The result is not one closed loop, but many.

This fragmentation is already visible in Europe. According to IAB Europe, the share of brands working with four to six Retail Media Networks more than doubled from 10% to 24%. At the same time, 53% of buy-side stakeholders cite a lack of standardisation as a barrier to investment, while 51% point to Retail Media Network fragmentation.

Interoperability itself is also becoming part of the problem. 34% of respondents identify a lack of interoperability between Retail Media Networks as a barrier, while 53% say Retail Media Networks are not sufficiently integrated with other technology.

The challenge is therefore becoming structural: advertisers want access to valuable retail signals, but they also need those signals to work across an increasingly fragmented media ecosystem.

Retail Data Is Starting to Travel

Several developments in the US market suggest that Retail Media Networks are beginning to experiment with more flexible boundaries.

Amazon provides one of the clearest examples. In July 2026, Amazon expanded its Omnichannel Metrics capabilities, allowing US advertisers to see how Amazon DSP campaigns drive sales at specific retailers outside Amazon. The measurement combines Amazon Shopper Panel signals with third-party data and provides retailer-level sales and unit information.

This is an important development because Amazon’s commerce intelligence is increasingly being used to understand outcomes beyond its own marketplace. The value of Amazon’s data is no longer limited to explaining what happens inside Amazon.

Walmart is experimenting with a different model. Through its collaboration with Google Display & Video 360, advertisers can activate Walmart Connect first-party audiences on YouTube and measure how those campaigns affect sales at Walmart.

In both cases, the traditional Retail Media boundary becomes more flexible. The retailer still controls its data, but that data can create value outside retailer-owned inventory.

The traditional model looked like this:

Retailer Data → Retailer Media → Retailer Transaction

An emerging model can extend further:

Retailer Data → External Media → Commerce Outcome → Connected Measurement

These initiatives remain early signals rather than evidence that walled gardens are disappearing. However, they suggest that some of the largest Retail Media players are exploring how their data can become more useful across the wider advertising ecosystem.

Europe Is Taking a Different Route

The US currently provides some of the clearest examples of direct platform interoperability. This is not surprising. Its Retail Media market is larger and more mature, which makes fragmentation a more immediate problem.

Europe faces a different environment. Retail Media is distributed across many national retailers, technology providers and regulatory frameworks. Building individual connections between every retailer and every advertising platform would therefore create considerable complexity.

The dunnhumby Network Alliance offers an interesting alternative. Launched in June 2026, the initiative includes pilots with Tesco, B&Q, John Lewis and Waitrose. It gives brands and agencies a single route to activate campaigns across multiple retailers while allowing individual retailers to maintain control of their media businesses.

Standardisation is developing alongside these commercial initiatives. IAB Europe has been working to create common definitions and measurement frameworks across the market. This matters because connectivity alone does not solve fragmentation. If every platform measures sales, attribution and incrementality differently, connecting more platforms could simply create more complexity.

The US and Europe may therefore be developing different responses to the same problem. The US is experimenting with direct connections between retailer data and large advertising platforms. Europe appears to be placing greater emphasis on common standards and multi-retailer collaboration.

This distinction could become particularly important for smaller European retailers.

Interoperability Does Not Mean Open Data

The concept of interoperability can easily create the wrong impression. Retailers do not need to make customer data freely available. Doing so could undermine one of the foundations of Retail Media.

First-party data remains a strategic asset. The real question is how retailers can increase the utility of that asset without losing control. This distinction is fundamental: open data is about access; interoperability is about controlled connectivity.

Technology can support that model. Data clean rooms, for example, can allow companies to analyse or match datasets without directly exchanging raw customer information. APIs can connect systems while maintaining defined permissions and access rules.

However, technology does not automatically solve interoperability. Different clean room environments can use different protocols and infrastructures. Connecting them can introduce another layer of technical and operational complexity.

In Europe, privacy regulation adds another dimension. GDPR principles such as purpose limitation and data minimisation mean that possessing first-party customer data does not automatically allow a retailer to use it for every advertising purpose or across every external environment.

Privacy, consent and governance therefore cannot simply be added after an interoperability model has been designed. They need to form part of the architecture itself.

The objective is not maximum data accessibility, but controlled interoperability based on clear permissions, purposes and governance.

The Retail Media Interoperability Value System

If interoperability becomes more important, retailers will need more than technology integrations. They will need a system that determines how data moves from ownership to activation and ultimately to measurement.

I see four capabilities at the centre of this system:

Data Ownership → Controlled Access → Cross-Platform Activation → Connected Measurement

1. Data Ownership

Retailers need a strong first-party data foundation. Transaction data, loyalty signals, product interactions and shopping behaviour create the intelligence behind Retail Media.

Without differentiated data, interoperability provides limited strategic value. Connectivity therefore does not replace the retailer’s data advantage. It builds on it.

2. Controlled Access

The second capability determines how external partners can use retailer data. This requires governance, permissions, privacy controls and technology infrastructure.

Retailers need to decide which signals partners can activate, where they can activate them and for which purposes. The objective is not maximum accessibility, but useful accessibility without losing control.

This may ultimately become the most strategic layer of the model because it defines the balance between data utility and differentiation.

3. Cross-Platform Activation

Retail data becomes more powerful when advertisers can use it across relevant media environments. On-site Retail Media will remain important, while off-site activation already extends retailer audiences into social platforms, connected TV and programmatic advertising.

Interoperability can take this further by connecting retail signals with the media buying environments that advertisers already use. This could reduce the need to operate every campaign through an isolated retailer platform.

4. Connected Measurement

Activation alone does not solve fragmentation. Advertisers also need to understand what happened after media exposure.

Connected measurement aims to link Media Exposure → Customer Behaviour → Commerce Outcome → Learning across different environments. The commerce outcome could happen on a retailer website, inside a physical store or through another measurable commerce environment.

As Retail Media expands beyond retailer-owned inventory, measurement will increasingly need to follow the same path.

Together, these four capabilities form what I call the Retail Media Interoperability Value System. The objective is not to maximise interoperability at every stage. Instead, it is to determine where connectivity creates incremental value without weakening the retailer’s control over its data.

The Cost of Interoperability

There is also a risk in assuming that greater interoperability will benefit every Retail Media Network equally.

Amazon and Walmart can invest heavily in identity infrastructure, APIs, clean rooms, measurement technology and integrations with major advertising platforms. A smaller national or regional retailer may not have the same resources.

Interoperability could therefore create another paradox. Instead of reducing concentration, it could make the largest Retail Media Networks even more attractive. Their audiences would not only be larger; they would also become easier to activate and measure across the wider advertising ecosystem.

The operational burden also matters. Data governance, consent management, technology integrations and measurement standards require investment and specialised capabilities. For smaller retailers, the cost of building these capabilities independently could outweigh the immediate commercial opportunity.

This is where the European approach discussed earlier becomes particularly interesting. Initiatives such as the dunnhumby Network Alliance, combined with shared measurement standards, could potentially lower the cost of interoperability by reducing the need for every retailer to build the same capabilities independently.

Instead of trying to recreate the infrastructure of Amazon or Walmart, smaller retailers could participate through shared frameworks, technology partners or common access models. Whether this approach can scale remains uncertain, but it highlights an important point: interoperability is not simply a technology upgrade. It is also an operating model decision.

Conclusion: From Data Ownership to Data Utility

Retail Media’s first competitive advantage came from ownership. Retailers combined customer data, media inventory and transactions inside controlled ecosystems, creating targeting and measurement capabilities that traditional advertising struggled to replicate.

As the market expands, however, advertisers increasingly need to operate across multiple Retail Media Networks and media platforms. The result is a growing tension between the value of closed ecosystems and the complexity created by having too many of them.

Amazon, Walmart and emerging European initiatives suggest that the industry is starting to experiment with different solutions. Some involve external activation and measurement. Others focus on common standards or multi-retailer collaboration.

None of these approaches means that the walled garden is disappearing. First-party commerce data remains too valuable for retailers to simply open their ecosystems.

Instead, the competitive question may be changing. Owning valuable commerce data is no longer the only advantage. Retailers increasingly need to decide how that data can create value beyond their own walls without weakening privacy, differentiation or control.

The next era of Retail Media may therefore not be about opening the walled garden.

It may be about deciding which doors to build, where to place them and who gets the keys.