We just shipped support for the ugliest part of HTTP: Vary – Cloudflare Blog

Cloudflare has launched support for the HTTP Vary header in its Cache Rules, allowing developers to control how caches handle requests that may produce different responses from the same URL. The Vary header tells intermediary caches which request fields (like Accept or Accept-Language) may affect a response, but it doesn't specify which differences actually matter—Cloudflare's new feature lets users normalize, pass through, or bypass caching based on each header's actual importance. This addresses a long-standing complexity in HTTP caching, where ignoring Vary risks serving incorrect content while treating every variation as distinct can create thousands of barely-reusable cache entries.