Chrome UX Report API is a newly released REST API that gives access to performance metrics of a page url. Metrics includes Chrome's Largest Contentful Paint (LCP), First Input Delay (FID), Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS).
The CrUX API only reports field data unlike PageSpeed Insights API that also additionally reports lab data. Field data is basically historical data collected from page loads experienced by users in the past. Lab data is basically data collected almost at that "live" instant.
Because CrUX API just need to provide historical data, it is quite fast. PageSpeed Insights API on the other hand needs to measure "live" performance metrics, so it takes some time to return back the results.
CrUX API is a fast way to get an idea of the performance metrics of any webpage. It is free, and just needs an API key.
Checkout Chrome UX Report API on Google Developers.