In Chrome 83, a bug was fixed in the implementation of First Input Delay (FID). Prior to M83, First input delay values less than 1ms were not reported to the Chrome User Experience Report (CrUX). These values have always been exposed in the web API.
For the CrUX data, developers often view it in terms of the percent of page loads which are “fast” (less than 100ms), “medium” (less than 300ms), or “slow” (greater than 300ms). Since events with times less than 1ms are now included, sites can expect to see an increase in the percent of fast sites. How much an individual site's metrics will be affected depends on the number of very fast devices loading pages and the baseline amount of work being done. Sites with more fast devices and less work during load will see the largest increase in fast page loads.
It's still important for sites to focus on the long tail of FID, working to bring down bad user experiences in high percentiles.
Data from the web API is unaffected by this change.
Chrome 83 is currently scheduled to release on May 19. This page will be updated with an improved estimate of how sites' metrics are impacted within two weeks of launch.