At a glance the headline numbers for HTTP protocol
The HTTP protocol of the HTML document response.
23.6% of HTML documents arrive over HTTP/3.
HTTP protocol who uses what, and how fast each group loads
Little daylight between the groups: every variant sits near 1.3s median LCP. computed
Passing LCP per HTTP protocol which group passes the LCP most often
No variant stands out: pass rates sit between 85% and 88%. computed
Why this matters for the Core Web Vitals, and where to start fixing it
The protocol decides how expensive a connection is. HTTP/3 sets up in fewer round trips and a lost packet no longer stalls everything behind it, which TCP-based protocols suffer from. The document request is where this matters most: it is the first request of the visit and it carries the whole TTFB.
There is a catch on the very first visit. Browsers often discover HTTP/3 support through a header on a previous response (Alt-Svc), so the first document fetch can still pay the older protocol's price. DNS HTTPS records fix that discovery, and your CDN controls whether they exist.
How does this affect the Core Web Vitals?
The choice barely moves the LCP: 88% pass at best, 85% at worst. This signal does not separate passing sites from failing ones.
Chrome field data from 189,915 sites, representing millions of real page loads. How we measured.