First-party data: why it went non-negotiable (and what really happened to cookies)

For years, the entire industry braced for the “death of third-party cookies.” Then, in July 2024, Google scrapped the plan — and in October 2025 it also shut down Privacy Sandbox, the set of APIs that was meant to replace them. Many breathed a sigh of relief: “so we don't have to change anything.” Wrong.

Because the real story was never about Google's decision. Third-party cookies are technically alive in Chrome, yet practically more and more useless: Safari and Firefox block them, ad blockers strip them out, opt-outs keep rising. The answer that works regardless of what Google does is the same one we recommended even before the reversal: first-party data. Here's why, and how.

What actually happened to cookies and Privacy Sandbox

The timeline matters, because a lot of bad decisions rest on it. In July 2024, Google announced it was dropping its plan to remove third-party cookies from Chrome. In April 2025, it confirmed: it won't remove them by default, moving instead to a model where the user can choose to block them, without a separate prompt — the default behavior stays unchanged.

Then, in October 2025, came the less-publicized but more strategically important blow: Google deprecated all 10 remaining Privacy Sandbox APIs — Topics, Protected Audience (formerly FLEDGE), Attribution Reporting and the rest. These were exactly the technologies the industry had been advised to prepare for over years. They're gone.

The confusing conclusion: third-party cookies didn't die, but their official replacements don't exist either. You're left with an old technology, alive but in decline, and no official path forward. That's not good news for the status quo — it's precisely why first-party data becomes non-negotiable.

Why “alive” doesn't mean “reliable”

Even where third-party cookies do work (Chrome, by default), real coverage is well below 100%. Safari and Firefox — together a significant slice of traffic — block them entirely. Intelligent Tracking Prevention shortens cookie lifespan. Ad blockers and privacy extensions are growing. And users who choose to block them are increasing. The result: third-party-cookie tracking sees a smaller and smaller share of reality, year after year.

From “having data” to “producing ROI”: activation

First-party data is worth nothing sitting in a warehouse. The value appears at activation — when you send the data back into the tools that make decisions. The mechanism is called reverse ETL: the inverse of classic ETL. Instead of bringing data into the warehouse, you push segments from the warehouse out to Google Ads, Meta, CRM and email.

Concretely: you sync your high-LTV customer list to the ad platforms to build lookalikes from it, exclude existing customers from acquisition campaigns, or trigger an email flow off real behavior. The reported numbers are consistent: reverse ETL is associated with acquisition-cost reductions of 15-30% and ROAS increases of 25-40%, turning ROI-positive in roughly three months. Moving from broad “all customers” lists to lookalikes segmented on high LTV alone delivers +20-40% ROAS.

This is where first-party data ties into the rest of the measurement stack: it needs server-side collection to be complete, and orchestrated consent to be compliant. They're the three pieces of the same system.

Conclusions

Google walking back cookie deprecation was read by many as a delay of the problem. It's the opposite: it confirmed no official savior is coming. Third-party cookies remain alive but in decline, and their replacements (Privacy Sandbox) have been abandoned. The only foundation that doesn't depend on someone else's decisions is first-party data.

And it isn't a defensive bet, it's one that pays: the acquisition-cost reductions and ROAS gains are documented, and the compliance advantage comes on top. The question for your business is no longer “what do we do when cookies disappear?” — it's “are we already using the data our customers hand us, or are we letting it sit in a warehouse?”