Safari 26.2 has started exposing Largest Contentful Paint (LCP) and Interaction to Next Paint (INP) via the Performance API. This is a significant development for anyone measuring real user metrics (RUM), and Shopify store owners may notice unexpected changes in their performance dashboards.
Nothing has actually changed for your users Jump to heading
This is the most important thing to understand: your site performance did not suddenly get worse (or better). The underlying user experience has always been what it is. We are simply now able to measure it.
For years, real Safari users were invisible in LCP and INP reporting because WebKit did not expose the relevant Performance API entry types used to observe these metrics in JavaScript. In practice, that meant no largest-contentful-paint entries (LCP) and no event entries (Event Timing, used for INP) in Safari. See LargestContentfulPaint and PerformanceEventTiming.
As more and more iPhone users update their devices, you may see a shift that reflects reality catching up with your measurements. The reality is, the new numbers will reflect the existing status quo, how your users are currently and have been experiencing your site. Nothing in that regard has changed. We're now just being given a tool to accurately measure it.
How much traffic are we talking about? Jump to heading
A significant portion of Shopify storefront traffic comes from WebKit-based browsers. This includes all iOS traffic (any browser on iOS uses WebKit under the hood, including Chrome, Instagram, and Facebook) plus Safari on macOS.
The percentage of WebKit traffic varies by store, with larger merchants typically seeing higher proportions of iOS users. Depending on your customer base, a substantial portion of your sessions may have been previously unmeasured for LCP and INP.
What to expect Jump to heading
Early feedback suggests:
Your sample sizes will increase significantly. This is a good thing. More data means more accurate percentiles and better visibility into actual user experience. It's like getting a new 8K Ultra HD (UHD) tv, all of a sudden you can see details more clearly, warts and all. The warts were always there, but now you get to see them in high def.
Your LCP scores will likely shift. Anecdotal evidence leads us to expect a moderate to major shift once Safari data is included. Some early reports suggest Safari LCP is slower than Chrome for the same page loads, but others are reporting faster LCP scores. There is not enough data yet to draw firm conclusions, so we're definitely monitoring what this looks like across the entire Shopify ecosystem.
INP changes are less predictable. The impact on INP scores is highly site-dependent and largely depends on your JavaScript implementation rather than the browser. How your scripts handle events, JS bundle size and complexity, and third-party code management all affect INP differently across sites, so this change to include INP in Safari might highlight new bugs or it might help shine more light on existing issues.
How to prepare Jump to heading
If you are using Shopify's web performance dashboards or any RUM tool, here are practical steps to take.
Segment your data by browser Jump to heading
Before Safari data floods your dashboards, establish baselines. Create reports that segment by browser family so you can compare Chrome and Safari performance separately.
Consider your RUM strategy Jump to heading
Do not rely on CrUX, Pagespeed Insights, etc., to be your source of truth anymore. Treat RUM as the source of truth for user experience. This is where it's super nice that Shopify provides free RUM data for all stores. The new LCP and INP metrics data from Safari, mPulse, etc., are already flowing right in. Learn how to use these reports in our guide to Mastering Shopify's Performance Reports. Other RUM providers like Speedcurve, etc., will also show more comprehensive data now that Safari is reporting these metrics, with minor changes necessary (if any).
Note on existing data Jump to heading
Real Safari data started with the beta release of Safari 26.2. Any prior "Safari" entries with LCP or INP values in your RUM data were not from actual Safari users.
What we still do not know Jump to heading
Safari's implementation is new, and the community is still gathering data. Some open questions:
- Are there implementation quirks or edge cases in Safari's LCP or INP reporting?
- How do specific optimization techniques perform on WebKit vs Blink?
- Will the gap between Safari and Chrome metrics narrow as more data comes in?
The bottom line Jump to heading
As far as web performance metrics go, this is exciting. We have wanted this capability for years. Sadly, Safari has garnered a slight reputation as "the modern IE6" because of its lagging standards implementations, so this is a welcome change.
For Shopify store owners: expect your RUM dashboards to shift. Do not panic. Segment your data, check your LCP images for lazy loading, and use the new visibility to make informed optimization decisions.
If you see unexpected changes in your Shopify web performance reports, reach out to us or check back here for updates.
