As shown in the commit itself[1] (and implied by the original article), the connection header always started with a constant text block. It was just changed to include &quot;PRISM&quot; instead of &quot;START&quot;.<p>[1] <a href="https:&#x2F;&#x2F;github.com&#x2F;http2&#x2F;http2-spec&#x2F;commit&#x2F;ac468f3fab9f7092a430eedfd69ee1fb2e23c944" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;http2&#x2F;http2-spec&#x2F;commit&#x2F;ac468f3fab9f7092a...</a> (as linked by others below)