The digital advertising ecosystem is undergoing one of the most significant transformations in its history. As third-party cookies phase out, the way brands reach consumers and how publishers monetize their audiences is shifting dramatically. For both advertisers and publishers, one strategy that stands resilient amid these changes is audience extension.
Audience extension is not a new concept, but in a cookieless world, it's gaining renewed importance. By leveraging first-party data, audience extension enables publishers to help advertisers reach their target customers across the open web---without relying on third-party cookies. For advertisers, it offers a trusted alternative to audience targeting. For publishers, it becomes a strategic asset in retaining ad dollars and enhancing value propositions.
This article explores how audience extension adapts to a cookieless world, what technologies enable it, and what both sides of the ecosystem need to do to succeed.
Audience extension allows a publisher to offer advertisers the ability to reach the publisher's users not just on the publisher's owned and operated (O&O) properties but across third-party sites and platforms.
Historically, this has relied on third-party cookies to track users and deliver ads elsewhere. But in a cookieless future, audience extension must lean on alternative forms of identity and permission-based data collection.
Google Chrome's plan to deprecate third-party cookies, following Safari and Firefox, is more than just a technical update. It affects:
How advertisers track and target users
How publishers monetize their audience
How performance is measured and attributed
This change demands a more privacy-conscious, durable solution for connecting advertisers with high-value audiences---and audience extension, retooled with first-party data, is one of the most viable paths forward.
Without third-party cookies, the most valuable data is data that comes directly from the user.
Publishers who collect information via:
Newsletter sign-ups
Subscription models
Account creation/login
On-site behavior
can segment users based on known interests and behaviors, and make these segments available for targeting across other environments.
From an advertiser's perspective, this data is more accurate, relevant, and privacy-compliant than the alternative datasets offered by third-party vendors.
In a cookieless world, identifying and matching users across platforms is no longer a given. This is where identity resolution becomes critical.
Some of the methods and tools include:
Hashed Email Matching: Matching anonymized email addresses across participating platforms
Universal IDs: Solutions like The Trade Desk's Unified ID 2.0, ID5, and LiveRamp's RampID
First-Party ID Graphs: Built by publishers to track users across their ecosystem
Contextual Signals + Consent-Based Enrichment: Using content and behavior data with user permission to infer identity and intent
These tools allow publishers to maintain addressability across the web and enable advertisers to continue precision targeting without cookies.
To offer viable audience extension solutions post-cookie, publishers must:
Build a Clean Data Layer: Segment users by behavior, context, demographics, and engagement.
Ensure Consent: Use transparent consent management platforms (CMPs) to gather and record permissions.
Partner Strategically: Work with DSPs, SSPs, and identity providers that support cookieless transactions.
Develop Activation Pipelines: Enable audiences to be activated through deals, platforms, or managed services.
The shift to audience-first, identity-resilient practices is not just a privacy requirement---it's a business opportunity.
Advertisers who previously relied on cookies for broad-based retargeting must now:
Prioritize direct relationships with premium publishers
Evaluate new identity and data providers
Test first-party data partnerships through audience extension
Shift measurement strategies toward incrementality, modeled attribution, and holistic performance
Working with publishers on audience extension allows advertisers to connect with high-value users while maintaining relevance, even in anonymous or semi-anonymous environments.
A regional health publisher builds audience segments for users interested in heart health, based on article reads and newsletter activity. By partnering with an identity provider using hashed emails, the publisher enables a pharmaceutical advertiser to reach these users across other premium health sites and apps.
No third-party cookies are involved. The audience is privacy-compliant, highly relevant, and capable of scaling through programmatic channels. The advertiser sees higher engagement, while the publisher generates revenue beyond their own media.
Whether you're a publisher or an advertiser, a successful cookieless audience extension setup requires several components:
Consent Management: To capture and manage user permissions
Data Management Platform (DMP/CDP): For building and segmenting audiences
Identity Graph or Partner: For resolving user identity across platforms
Programmatic Activation: Via DSPs or SSPs that support first-party and cookieless signals
Analytics and Reporting: To monitor campaign effectiveness and compliance
There is no one-size-fits-all identity solution, making interoperability a challenge.
Solution: Support multiple ID systems and test combinations to see what performs best.
First-party audiences are typically smaller than third-party pools.
Solution: Focus on quality and performance; expand through partnerships or publisher networks.
Many advertisers are still learning how cookieless audience extension works.
Solution: Publishers should simplify their offering and demonstrate performance through test campaigns and case studies.
While the loss of third-party cookies disrupts old ways of doing business, it also encourages better practices:
Less reliance on opaque data marketplaces
More value for high-quality publishers
Stronger advertiser-user relevance
Greater transparency and compliance
Audience extension is positioned to thrive in this environment because it is built on trust: between user and publisher, and between advertiser and media partner.
In a cookieless world, audience extension becomes more strategic, not less. Publishers who own strong audience relationships will become even more valuable to advertisers. And advertisers who embrace this model can continue targeting with confidence, reach with efficiency, and perform with integrity.
Rather than seeing the cookie's demise as a threat, the smartest players in the space will see it as a chance to build better, more sustainable marketing ecosystems.
Audience extension is not just surviving in this new world---it's redefining what comes next.