In a landmark update for the modern web development ecosystem, Google has officially introduced experimental versions of the three Core Web Vitals—Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS)—within the Chrome User Experience Report (CrUX). This move represents a significant evolution in how Google measures the performance of Single-Page Applications (SPAs), moving away from the traditional, rigid "hard load" tracking that has historically penalized dynamic web experiences.
By accounting for "soft navigations"—the in-app page transitions that occur without a full browser reload—Google is finally providing developers with a more accurate, nuanced picture of how users actually experience their sites. Available as of the October 13 release, this data can be accessed through BigQuery, the CrUX API, the History API, and the CrUX Vis dashboard.
The Evolution of Measurement: Why Soft Navigations Matter
For years, the gold standard for web performance measurement has been the "hard load." When a user navigates to a new page, the browser clears the memory, fetches new HTML, CSS, and JavaScript, and renders the page from scratch. However, the rise of frameworks like React, Vue, and Angular has shifted the paradigm toward SPAs.
In an SPA, the browser loads the core application shell once. Subsequent "page changes" are handled dynamically; the site uses JavaScript to fetch new data and swap out the view while the URL updates in the address bar. Previously, CrUX treated these subsequent interactions as part of the initial landing page session. This meant that if a user spent ten minutes on a site, performing five different "soft" navigation actions, all of the layout shifts and interaction delays were essentially "blamed" on the initial load or lumped into a single, muddy data set.
Defining the "Soft Navigation"
Under the new framework, powered by the Soft Navigations API (which has been active by default since Chrome 151 on July 28), a "soft navigation" is defined by two specific triggers:
- A user action: A click or interaction that initiates a change.
- Visible indicators: A change to the URL and a visible paint (rendering of content) on the screen.
By isolating these events, Google can now attribute performance metrics to the specific destination URL, rather than forcing all metrics back to the entry point. This ensures that the data accurately reflects the user’s experience at the moment they arrive at a specific "page" within the application.
Chronology: From Origin Trials to Experimental Integration
The journey to this integration has been methodical and transparent.
- August 2025: Industry observers and developers began testing the waters of the Soft Navigations API through a public origin trial. At this time, it was clear that the existing metrics were failing to represent the realities of modern web architecture.
- July 28, 2025: Chrome version 151 was released, turning the Soft Navigations API on by default. This provided the necessary infrastructure for the browser to start "labeling" these events correctly.
- October 13, 2025: The major CrUX update arrived. For the first time, three new fields were added to the dataset:
experimental_largest_contentful_paint_with_softnavs, along with experimental versions for INP and CLS. - May 2027 (Target): Chrome has set a tentative goal to move these metrics out of their "experimental" status. Between now and then, the data will be subject to developer feedback and iterative refinement. Once the status changes, Search Console is expected to adopt these metrics as the new standard for reporting.
Supporting Data: How the Web Changes Under the New Lens
Google’s analysis of the current web landscape reveals that the impact of this change is highly dependent on the architecture of the site.
Who is Affected?
For the majority of the web, this update will be a non-event. Roughly 70% of origins in the CrUX dataset have little to no soft navigation traffic. These are primarily traditional multi-page websites (MPAs) that perform a full reload on every click. For these sites, the "experimental" metrics will yield results nearly identical to the "stable" metrics.
However, for sites that rely on SPAs, the change is transformative. Among the top 1,000 websites on the web, approximately 35% on Android and 42% on desktop rely on soft navigations for more than half of their page views. For these sites, the experimental metrics provide a far more optimistic—and arguably more accurate—view of performance.
Performance Gains
The most striking data point comes from Android origins where 75% to 100% of page views are soft navigations. Under the old stable metric, only 26% of these sites passed the "Good" threshold for LCP. Under the new experimental metric, that pass rate jumped to 87%.
As Annie Sullivan of the Chrome team noted, this is not because SPAs have suddenly become faster than MPAs, but because the new measurement methodology correctly identifies that "follow-up clicks" are naturally faster than initial page loads. By grouping these events appropriately, the data stops unfairly penalizing the "initial load" metrics for every subsequent interaction that happens during a session.
The Impact on INP and CLS
- INP (Interaction to Next Paint): The new measurement tracks responsiveness per page view rather than the slowest interaction across the entire session. This has roughly doubled the Android pass rates for SPA-heavy sites. However, Google warns that heavy JavaScript execution during these transitions can still negatively impact INP.
- CLS (Cumulative Layout Shift): By grouping shift events by "view" rather than "session," the experimental metrics put SPA-heavy desktop sites on par with traditional multi-page sites, effectively correcting a long-standing measurement bias.
Official Responses and Developer Guidance
The sentiment from the Chrome team is one of cautious optimism. Annie Sullivan’s guidance to developers is clear: "If your site doesn’t use JavaScript to dynamically swap out page content and update the URL without a full browser reload, you shouldn’t expect to see any changes in your metrics."
For those who do manage SPA-heavy sites, the advice is to use the new "Include soft navigations" toggle in CrUX Vis. This tool allows developers to conduct side-by-side comparisons of their current stable scores and the new experimental ones. This transparency is intended to help developers understand which specific areas of their site are meeting the threshold and which are still struggling.
However, Google emphasizes that the experimental status is not merely a label; it is a warning. The metrics are expected to shift from month to month as the underlying measurement algorithms are refined. Developers are encouraged to participate in the feedback process via the web-vitals feedback group or the Soft Navigations GitHub repository.
Implications for the Future of SEO and Web Development
The transition of these metrics from "experimental" to "standard" in 2027 will likely have profound implications for Search Engine Optimization (SEO).
1. Leveling the Playing Field
Historically, SPA developers have often felt that Core Web Vitals were biased against them, as the "first load" metrics were disproportionately influenced by the complexity of the initial JavaScript bundle. By adopting these new metrics, Google is essentially admitting that the "Web Vitals" framework must evolve to accommodate the way the modern web is built, rather than forcing the web to conform to a legacy measurement model.
2. A Call for Quality Control
While the new metrics offer a more "forgiving" way to measure SPA performance, they also place the burden of proof on the developer. Because the browser is now specifically tracking these events, developers must ensure that their "soft navigation" triggers are correctly implemented. If a site updates the URL but doesn’t properly report the "paint" completion, or if it triggers fake navigations, the data will be inaccurate.
3. Long-Term Strategy
The November CrUX release is already slated to include further updates, specifically the addition of First Contentful Paint (FCP) and refined navigation types. This ongoing evolution suggests that Google is committed to a multi-year strategy of refining how we quantify "user experience."
For developers and site owners, the next 18 months represent a period of observation. While it is not yet time to overhaul SEO strategies based on these experimental numbers, it is the perfect time to audit SPA-heavy sites to see how they perform under the new criteria. As these metrics move toward becoming the official standard, those who have optimized their soft navigation transitions will likely find themselves ahead of the curve when the official Search Console transition occurs in 2027.
Ultimately, this update is a recognition of reality. The web is no longer a collection of static documents; it is a platform for interactive applications. By finally measuring those applications on their own terms, Google is ensuring that its performance metrics remain relevant in a world where the "page load" is becoming a thing of the past.
