What was the Chrome Topics API, and what replaces it in a plan?

What was the Chrome Topics API?

Google's own overview of the Topics API (opens in a new tab) described it as a mechanism designed to allow for interest-based advertising without sharing the specific sites a user has visited across the web. In place of a cookie that followed a person from site to site, the browser kept the history locally, worked out a short list of interests, and handed a few of them to ad tech scripts that asked.

The Chrome Platform Status entry (opens in a new tab) records an origin trial that began in Chrome 101 and the API being enabled by default in Chrome 115. The same entry summarizes the intent: give callers coarse-grained advertising topics that the page visitor might currently be interested in, to supplement the contextual signals from the current page. That phrase matters for buyers, because it shows Topics was designed to sit beside context, not to replace it.

How did Topics differ from reading the content of a page?

Topics looked backward at a person's browsing. Contextual targeting looks at the page in front of them. The explainer is explicit that interests were chosen based only on website hostnames, rather than the full URL or the contents of visited websites. A classifier, which the explainer says Google trained on human curated hostnames and topics and shipped with Chrome, mapped each hostname to topics from a list the initial design put at about 350 entries.

• Weekly epochs: for each week, the browser calculated the person's top five topics from browsing information kept on the device.
• Three topics at most: a call returned up to three topics, one from each of the preceding three weeks, in random order.
• Observed callers only: a caller received a topic only if it had observed the person on a site about that topic within the past three weeks.
• Noise on purpose: there was a 5 percent chance per person, site and week that a random topic was returned instead.
• Empty by design: opting out, browsing in incognito mode or clearing history left the list empty.

The hostname rule had a practical consequence. A large city newspaper's site carries recipes, election coverage and car reviews, yet Topics saw only the hostname, so a visit to its recipe page counted the same as a visit to its politics desk. Reading the page itself is the only way to tell those visits apart, which is the work our semantic targeting guide describes.

Which Privacy Sandbox technologies did Google say it would retire?

In its October 17, 2025 update (opens in a new tab), Google said it would retire Privacy Sandbox technologies including Topics, Protected Audience and the Attribution Reporting API. The post, by Anthony Chavez, Google's vice president for Privacy Sandbox, says the decision followed an evaluation of ecosystem feedback about their expected value and came in light of their low levels of adoption. It lists Topics for both Chrome and Android, and says Google will follow Chrome and Android processes for phasing the technologies out.

The full retirement list and the few technologies Google kept are set out in our guide to cookieless advertising, together with the browser cookie context. For Topics specifically, the dates that followed are recorded in Chrome's own engineering process. On November 7, 2025 a Chrome engineer posted an Intent to Deprecate and Remove: Topics API (opens in a new tab) on the public blink-dev list, estimating deprecation in Chrome 144 and removal in Chrome 150. A follow-up on June 11, 2026 said the API had been deprecated in Chrome 144 and proposed a staged removal running through Chrome 152.

What happens to plans that relied on Topics?

Any targeting, segment or measurement that drew on Topics loses its input once Chrome removes the API as proposed, and on Android as Google phases the Android version out. The loss can be hidden, because Topics could feed an interest segment or a bidding model inside a buying platform rather than appear as a line item of its own. The work is to find where it was used, decide what replaces it, and reset any comparisons that assumed it would continue.

Where should buyers check the current status of Privacy Sandbox APIs?

Google keeps several records, and they are written for different readers. The table lists what each one is and what it showed for Topics when we read it on October 22, 2026. Treat a vendor's summary as a pointer to these pages, not a replacement for them.

What does PlacementGraph read to judge context?