Immutable Response

A Cache-Control extension (Cache-Control: immutable) that tells browsers the response body will never change for the duration of its max-age, allowing the browser to skip conditional revalidation requests entirely during that window. Immutable is ideal for versioned static assets where the URL contains a content hash — the resource changes only when its URL changes. This eliminates unnecessary If-None-Match and If-Modified-Since round trips on page reload.