CrUX (Chrome UX Report)
Google's public record of how real Chrome visitors experienced your site.
What it is
The Chrome User Experience Report is Google's dataset of real-user performance collected from Chrome users who share usage statistics. Each metric is reported at the 75th percentile over a rolling 28 days. It is the field data at the top of PageSpeed Insights and the source of Search Console's Core Web Vitals report.
Why it costs you money
Lighthouse scores are a lab test on one simulated phone; CrUX is what your customers actually got, and it is the version Google uses. A page without enough traffic has no CrUX data of its own and is judged on the whole site's numbers instead.
How to check it yourself
Run a URL through PageSpeed Insights or our speed check and read the field-data section first. A fix shows up there gradually, because the 28-day window has to roll over before the old visits drop out.