Signed Exchanges: A Performance Win Worth Measuring
Since Cloudflare turned on support for Signed Exchanges (SXG) roughly nine months ago, the web platform specification has been quietly working to change how cached content is delivered. SXG lets third parties such as search engines deterministically verify and serve a cached version of your site, cutting the distance between user and origin. The result is faster load times, particularly for users on slower connections or in regions far from your servers.
The performance upside is real. Google’s experiments show that SXG-enabled prefetches trim between 300ms and 400ms off Largest Contentful Paint (LCP). Faster pages typically mean lower bounce rates and better SEO, and with Cloudflare’s one-click Automatic Signed Exchanges, you get that without wrestling with the open source toolkit.
What Real World Data Shows
With Chromium on Android supporting SXG for several months, we took a look at the actual performance changes customers are seeing. Across the 500 most-visited sites with Automatic Signed Exchanges enabled, 425 of them — 85 percent — saw an improvement in LCP, the Core Web Vital most tied to SEO impact.
The numbers hold up on other metrics as well: 389 sites (78 percent) improved their First Contentful Paint (FCP), and 489 sites (98 percent) saw better Time to First Byte (TTFB). That TTFB improvement is notable because after a prefetch, the resource sits in the client’s browser cache, so TTFB approaches zero when the user clicks through.
The median customer gained over 20 percent across these metrics, with some seeing gains up to 80 percent. Still, a few sites saw no improvement or a slight regression.
One culprit behind those stragglers was server-side personalization — SXG didn’t originally work with serving different HTML to logged-in users. That changed today with Google’s “Dynamic SXG,” which selectively enables SXG only for visits from cookieless users. Dynamic SXG is ready now: add a Vary: Cookie annotation to the HTTP header on pages using server-side personalization.
A note: client-side personalization, such as lazy-loading, is fully compatible with SXG.
To gauge Core Web Vitals for your own audience, a real-user monitoring tool like Cloudflare’s free, privacy-first Web Analytics can give you the picture.
SXG Extends to Desktop Browsers
Starting today, Chromium-based desktop browsers — Chrome, Edge, and Opera — will serve Signed Exchanges. If you’ve already enabled Automatic Signed Exchanges in your Cloudflare dashboard, nothing else is needed; desktop browsers start getting the SXG version automatically. Google estimates this change will roughly double SXG’s reach for your site’s traffic.
For those who haven’t yet flipped the switch, Automatic Signed Exchanges is available under the Speed > Optimization link in the Cloudflare dashboard.
