First-id and Decentriq: from data collaboration to media activation

This initiative is built on First-id's identifier, already widely adopted by French publishers. This setup enables audience matching within Decentriq's data clean rooms and simplified generation of lookalike audiences.

The Hachette Livre group, France's leading book publisher, wanted to launch three cleanroom activations with leading French media companies — Reworld Media, RMC BFM Ads, and Prisma Media — as part of an innovative data marketing approach, using First-id IDs identified on the hachette.fr and larousse.fr websites. The results were highly informative, thanks notably to good match rates (up to 43% for certain segments).

“We wanted to test a data clean room in partnership with powerful media companies to better understand our digital audiences, in strict compliance with GDPR,” explains Anais Prost, Data Marketing Manager at Hachette Livre. “This partnership gave us access to numerous high-quality audience insights that we had never had before — and the ability to activate them immediately. Via First-id identifiers, we had the opportunity to easily activate lookalike audiences.”

From matching to activating: Clean room insights in action

Each activation began with securely matching Hachette Livre's website visitors with publisher-side audiences using First-id as the matching key.

Inside Decentriq’s data clean room, these matched users were then analyzed to uncover audience overlap and top affinity segments between Hachette Livre and each publisher. These insights in turn helped create three high-performing lookalike audiences, each built directly within the clean room using publishers’ rich first-party data. 

To make this possible, Decentriq’s AI-powered modeling tools uncovered the top 5% most similar users to Hachette Livre’s customers within each publisher’s user inventory. These lookalikes were activated across all major browsers, including Safari and Firefox, using programmatic direct deals made possible thanks to Equativ. 

The visit rate observed on the hachette.fr and larousse.fr sites was 2.4 times higher for activated lookalike audiences, with a peak of 3.7x for Safari users.

“This collaboration not only proves the possible democratization of data collaboration for insights purposes but offers a simple solution for effective activation of these insights,” says Valentine Weyert, Chief Growth Officer of First-id. 

“The volume and richness of our data played a key role in the success of this activation. This confirms that activating a clean room is simultaneously simple, fast, and a source of immediately actionable insights,” emphasizes Marion Collombat, Chief Data Officer at Reworld Media.

“Working with First-id and Decentriq gave us a new way to monetize our audiences,” says Paul Ripart, Director Digital and Data at Prisma Media. “And to do it in a way that’s privacy-forward and efficient for advertisers like Hachette Livre.”

Despite multiple parties and platforms, the process was executed at speed.

“This initiative demonstrates that it's possible to combine marketing performance with respect for privacy. As a media sales house, we played a key role in orchestrating these complex data activations, with real demands on interoperability and efficiency,” adds Sibyl Georges-Picot, Director Data at RMC BFM Ads. 

Closing the loop with attribution in the clean room

For the next phase of their partnership, First-id and Decentriq are planning to jointly offer closed-loop measurement by reconciling post-campaign site traffic with media exposure, attribution, and incrementality — thus offering a full end-to-end solution for cookieless targeting to advertisers like Hachette Livre.

“It’s exciting to see publishers and advertisers in France embracing clean rooms not just for compliance, but for real business outcomes,” says Pierre Cholet, Chief Customer Officer at Decentriq.