Vercel has changed its CDN behavior so that origin responses with a Vary header that includes Cookie are served but not stored in the shared edge cache.

The company said the change is intended to avoid creating large numbers of low-value cache entries when cookies carry visitor-specific values. In Vercel’s logs, affected responses show vary_key_denied:cookie; the response header will report x-vercel-cache: MISS.

For hosting teams, the update is a useful reminder that personalization and shared caching need explicit boundaries. If a page is identical for all visitors, Vercel recommends removing Cookie from the Vary header so the CDN can cache it under the normal rules. If the response is personalized, operators should keep cookie variation and use Cache-Control: private to keep user-specific content out of a shared CDN cache.

The change is narrow: Vercel says caching behavior for other supported Vary headers is unchanged. The practical impact is most likely to show up on frameworks, plugins, or origin middleware that add broad cookie variation even when the final HTML or asset response is not actually personalized.

Source: Vercel changelog: “Vercel CDN no longer caches responses with Vary: Cookie”.