If your website relies on smooth, seamless transitions - like product filters, search results, or tab switches - especially in a Single Page Application (SPA), there’s an important Google update that's flying under the radar..

Starting with Chrome 139, Google is rolling out a new origin trial for its Soft Navigations API - an improved version of an earlier experiment that’s been refined based on developer feedback.

This isn’t a brand-new launch or a finalized web standard. Instead, it’s an API that’s evolving, aimed at solving a very real problem: how do we measure performance when users navigate your site without actually loading a new page?

Let’s unpack what’s changing - and why it matters, even if you’re not a developer.

What’s a “soft navigation,” and why should you care?

Most modern websites don’t reload the whole page every time a user clicks. Instead, they use JavaScript to update parts of the page instantly - whether that’s switching between tabs, opening a product quick view, or filtering search results.

This is what’s called soft navigation. It feels like a new page to the user, but technically, the browser thinks you're still on the same page. That means key metrics,like Largest Contentful Paint (LCP), don’t get reset, and don’t get tracked properly.

So the user might experience a lag or delay, but your analytics tools won’t see it.

Why this matters for Core Web Vitals?

Core Web Vitals - like LCP, INP, and CLS - are Google’s way of measuring real user experience. They directly impact your SEO rankings, ad visibility, and user engagement.

The problem? These metrics were originally designed for traditional page loads.

For SPAs and app-like sites, many of your most important user journeys happen without a full reload - and that means performance blind spots.

Chrome’s Soft Navigations API is an attempt to fix that - not by asking developers to flag these navigations manually, but by giving the browser the intelligence to detect them based on what the user is doing.

What’s new in this updated origin trial?

The earlier version of this API tied soft navigations directly to a reset of LCP. This latest version decouples those concepts, taking a more flexible and modular approach.

Here’s what’s changed:

• Soft navigations are now detected using a consistent heuristic - based on user interaction, DOM changes, and URL updates.

• A new metric, Interaction to Contentful Paint, is introduced to help measure performance after a soft navigation or user-triggered event.

• Performance entries (like LCP, INP, and CLS) now include a navigation identifier, making it easier to attribute performance to the right part of the user journey - even if the URL has changed by the time the metric is recorded.

In short, this update gives developers (and the browser itself) more accurate tools to track user experience inside SPAs.

What’s a “heuristic,” and why is Chrome using one?

Instead of asking frameworks like React or Vue to tell the browser when a soft navigation happens, Chrome is using a heuristic-based approach. That means it watches for certain patterns, like:

• A user clicks or taps

• The page updates visually

• The URL changes (via pushState or replaceState)

If these things happen together, Chrome assumes a soft navigation has occurred.

This makes the detection more consistent across different sites and frameworks - which is key if Google ever wants to use this data in tools like CrUX (Chrome User Experience Report) or Search Console. But it’s still an experiment, and Google is actively looking for feedback on whether these rules work well in real-world cases.

Why this matters for marketing, product, and business teams?

Even though this is a developer-facing API, it connects directly to outcomes that matter to your bottom line. Here’s how:

• More complete performance data: Until now, many in-page user journeys weren’t measured properly. That gap is closing.

• Better visibility for SEO and UX: If Google adopts this approach in CrUX or PageSpeed Insights later, your “invisible” performance issues might soon show up in reports that influence rankings.

• Smoother optimization loops: Teams working on conversion rate optimization or funnel performance will finally be able to track and diagnose slowdowns across more granular flows.

If your team has ever said, “This part of the app feels slow, but we can’t see it in our tools,” this is for you.

What should you do next?

This is still a work-in-progress, and Chrome wants developer feedback before moving forward. But this is a great moment to:

• Talk to your dev team about joining the origin trial if your site is a SPA or behaves like one.

• Audit key user flows that happen without page reloads - these will benefit most from the improved tracking.

• Keep an eye on updates from Chrome and performance tool vendors (like web-vitals.js) as the API matures.

You can test the API with local Chrome flags or register for the origin trial to use it with live users.

Final thought

This updated Soft Navigations API marks a thoughtful step forward from the Chrome team - one that acknowledges the evolving nature of modern websites and the need for better measurement tools. While still experimental, it reflects a clear direction: making performance metrics more reflective of real user experiences, especially on SPAs.

At Uxify, we’re excited to see these kinds of improvements. They align closely with our mission to make every user journey fast, measurable, and meaningful - and we’re looking forward to seeing how the API develops with feedback from the broader community.

If your site relies on smooth, app-like interactions, this is a great moment to get involved, share feedback, and help shape the future of how web performance is measured.