title: Why does Chrome use sec-ch-ua: "\"Not\\A;Brand";v="99"?
body: <p>I understand that making <a href="https://github.com/WICG/ua-client-hints" rel="noreferrer">user-agent hints</a> more ambiguous is intended, in part, to make <a href="https://panopticlick.eff.org/" rel="noreferrer">browser fingerprinting</a> harder.</p>
  <p>My own (Windows desktop) Chrome sends the headers:</p>
  <pre><code>user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36
  sec-ch-ua: &quot;Chromium&quot;;v=&quot;86&quot;, &quot;\&quot;Not\\A;Brand&quot;;v=&quot;99&quot;, &quot;Google Chrome&quot;;v=&quot;86&quot;
  sec-ch-ua-mobile: ?0
  </code></pre>
  <p>What I don't get is:</p>
  <ol>
  <li>Why the string &quot;Not A Brand&quot; specifically? Does anyone else use this pseudo-UA? Is this a joke of some sort?</li>
  <li>Why the <code>\&quot;</code> and <code>\\A;</code> inside the string? My only guess is that this is supposed to mess with parsers somehow (like the anti-IE hacks in CSS), but that seems like a rather odd purpose — and IIRC, <code>\A</code> is the bell character.</li>
  <li>How is this supposed to accomplish user-agent hint ambiguity, given that it <em>also</em> sends the full <code>user-agent</code> header, which has the specific version numbers?</li>
  <li>While at it: why does Chrome's user-agent also claim to be Mozilla, AppleWebKit, and Safari? It isn't, and this <code>user-agent</code> string is distinctively Chrome's. Does it have some sort of embedded components from those other browsers?</li>
  </ol>