Chrome has something like this called SDCH, but it hasn&#x27;t seen a ton of adoption outside Google:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;SDCH" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;SDCH</a><p><a href="https:&#x2F;&#x2F;engineering.linkedin.com&#x2F;shared-dictionary-compression-http-linkedin" rel="nofollow">https:&#x2F;&#x2F;engineering.linkedin.com&#x2F;shared-dictionary-compressi...</a><p><a href="https:&#x2F;&#x2F;aprescott.com&#x2F;posts&#x2F;sdch" rel="nofollow">https:&#x2F;&#x2F;aprescott.com&#x2F;posts&#x2F;sdch</a><p>Guessing part of the hurdle is that you can&#x27;t simply drop it in like gzip; you have to generate a dictionary and serve it and refresh it now and then (the LinkedIn post explains). And a CDN can&#x27;t just cache &quot;the SDCH&#x27;d version&quot; of a resource; ideally it&#x27;d cache one version for each recently used dict.<p>The other, slightly happier &quot;problem,&quot; is that other tuning can make the additional gains from SDCH less dramatic. I looked, and the Google homepage has a blob of JS that&#x27;s 40KB gzip+sdch&#x27;d--but it&#x27;s ~100KB gzip -9&#x27;d, and probably costs me 0KB most of the time because it&#x27;s cacheable and its Last-Modified is about a month ago.<p>CloudFlare&#x27;s Railgun proxy does use delta coding to good effect, though in a much different context (origin server to edge location).<p>I can imagine other variations, like priming Brotli&#x27;s (de)compressor&#x27;s history buffer with the first bytes of the old version of a cacheable resource in an If-None-Match request, if both sides have the old version handy and advertise the encoding. Sounds like what you&#x27;re saying. Like SDCH, that still isn&#x27;t drop-in; the server has to remember old versions of things. And it only applies to cached resources.<p>Anyhow, interesting space.