files/en-us/web/http/reference/headers/sec-ch-ua-bitness/index.md
{{SeeCompatTable}}{{SecureContext_Header}}
The HTTP Sec-CH-UA-Bitness {{Glossary("request header")}} is a user agent client hint which provides the "bitness" of the user-agent's underlying CPU architecture.
This is the size in bits of an integer or memory address—typically 64 or 32 bits.
This might be used by a server, for example, to select and offer the correct binary format of an executable for a user to download.
<table class="properties"> <tbody> <tr> <th scope="row">Header type</th> <td> {{Glossary("Request header")}}, <a href="/en-US/docs/Web/HTTP/Guides/Client_hints">Client hint</a> </td> </tr> <tr> <th scope="row">{{Glossary("Forbidden request header")}}</th> <td>Yes (<code>Sec-</code> prefix)</td> </tr> </tbody> </table>Sec-CH-UA-Bitness: <bitness>
<bitness>
"64", "32".A server requests the Sec-CH-UA-Bitness header by including {{HTTPHeader("Accept-CH")}} in a response to any request from the client, using the name of the desired header as a token:
HTTP/1.1 200 OK
Accept-CH: Sec-CH-UA-Bitness
The client may choose to provide the hint, and add the Sec-CH-UA-Bitness header to subsequent requests.
For example, on a Windows based 64-bit computer, the client might add the header as shown:
GET /my/page HTTP/1.1
Host: example.site
Sec-CH-UA: " Not A;Brand";v="99", "Chromium";v="96", "Google Chrome";v="96"
Sec-CH-UA-Mobile: ?0
Sec-CH-UA-Platform: "Windows"
Sec-CH-UA-Bitness: "64"
{{Specifications}}
{{Compat}}