Major agencies are investing in ID and data solutions, with WPP’s purchase of InfoSum the latest acquisition. In her latest feature, Shirley Marschall looks at the real reason why the ad tech arms race is really hotting up…

What do these recent announcements have in common?

• Publicis acquires Lotame, a long-standing identity provider.
• GroupM promises AI can seamlessly stitch together client, platform, and retailer data.
• WPP acquires InfoSum, an independent data clean room platform.

At first glance, not much.

On second glance, the strategies may differ but behind the vision of data harmony and algorithmic efficiency lies a direction: agencies are no longer content to facilitate data flows; they want to sit at the center of them.

Or more directly: they want hands-on access to brands’ first-party data.

ID, AI… The tools shift. The stories evolve. But the ambition doesn’t pause, it adapts.

From optimisation to ownership

Historically, agencies accessed client data for one purpose: campaign optimisation. The access was limited, tightly governed, and often “read-only.”

But that’s changed: AI needs training data, identity graphs need onboarding data and retail media demands transaction-level granularity.

Today, data isn’t just an input, it’s the engine. And agencies aren’t just accessing it, they’re building proprietary tools, training models, and monetising the outputs.

First-party data is now the most valuable asset in the ecosystem. And agencies are positioning themselves to hold the keys.

Old playbooks, new justifications

GroupM’s Choreograph was an earlier attempt to build a proprietary identity and data platform, designed to unify and activate first-party data at scale. The objective was clear: own the pipes that connect brand data to media outcomes.

Now, GroupM’s CEO Brian Lesser is pitching something bolder:

"We can connect first-party data from clients, platforms and retailers."

The promise? AI will do the stitching. The agency will sit in the middle. Seamless. Scalable. Smart.

Publicis is taking a different route, acquiring an established player instead of building one. With Lotame’s infrastructure and Epsilon’s data, Publicis claims clients can now connect with over 90% of consumers worldwide, powered by the Groupe’s proprietary CORE AI.

Arthur Sadoun, Chairman and CEO of Publicis Groupe, framed it bluntly:

"In the age of AI, the name of the game is connect or die."

But that begs the question:

Who’s really fighting for survival here?

Agencies keep reaching. Brands keep pushing back.

GroupM’s journey, from launching Choreograph to partnering with InfoSum to now acquiring it outright and pivoting to AI, is a case study in relentless positioning. Different strategies, same destination: closer proximity to brand-owned data.

First they built. Then they partnered. Now they own.

The language changes. The logic doesn’t.

Whether it’s ID graphs, clean room infrastructure, or AI-powered connectors, the goal remains the same: control the connective tissue of data activation and keep it proprietary.

But while agencies experiment with new ways in, brands have responded by fortifying the perimeter.

From on-premise CDPs to carefully governed clean rooms, many have built infrastructures designed not just for compliance, but for control. Clean rooms weren’t just privacy solutions; they were boundaries, a way to collaborate without handing over custody.

Both sides are digging in, just in very different ways.

That’s the heart of the tension:

Agencies keep finding new routes in. Brands keep inventing new ways to say no.

This isn’t a story about identity.

It’s a story about ownership.

And AI may be the most elegant excuse yet to centralise the stack.

The new middleman

Agencies were once trusted as impartial media middlemen, experts in planning and optimisation. But the deprecation of third-party cookies and the explosion of AI are redrawing those lines.

Now, they’re not just managing buys or reports. Not just building dashboards or bidding algorithms but going after the one thing every player wants: first-party data. They’re building infrastructure, the very platforms that determine how targeting, measurement, and creative delivery work.

When that happens, agencies shift from advisor to operator.

From service to stack.

Trust gets complicated

The tension this creates is real. Brands have grown increasingly cautious of proprietary tools from their agencies, questioning whether transparency and objectivity can survive when incentives conflict. Even identity providers risk losing perceived neutrality when absorbed by a holding company.

The IAB’s State of Data 2025 report underscores the unease:

“51% of brands are concerned about a lack of transparency into how agency/publisher partners use AI on their behalf.

52% of agencies are concerned that brands will bring AI in-house and reduce reliance on partners.”

This isn’t a perception gap. It’s a trust chasm.

This isn’t just about access. It’s about control.

As agencies embed themselves deeper into the layers that connect data to decisioning - AI, identity, measurement - the core question becomes:

Who controls the algorithms?

Who owns the outputs?

And who benefits when all of it runs through a single, agency-owned lens?

The future isn’t about the tools brands use.

It’s about who they trust to run them.

The bottom line: First-party data still belongs to the brand

Managing data is one thing. Monetising it is another. Owning it is everything.

Whether stitched together by AI, IDs, or clean room collaborations, brands expect neutrality in how their data is handled. If agency-owned stacks begin to feel like lock-in strategies, the market will shift - toward in-house teams, independent infrastructure, or more transparent partners.

Because no matter how advanced the algorithm, trust isn’t built by code. It’s earned.