Headers: Sec-CH-UA-Bitness

Sec-CH-UA-Bitness header

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

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See full compatibility

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

The HTTP Sec-CH-UA-Bitness 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.

Header type	Request header, Client hint
Forbidden request header	Yes (`Sec-` prefix)

Syntax

Sec-CH-UA-Bitness: <bitness>

Directives

<bitness>: A string indicating the underlying platform architecture bitness, such as: "64", "32".

Examples

Using Sec-CH-UA-Bitness

A server requests the Sec-CH-UA-Bitness header by including 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

Specification
User-Agent Client Hints> # sec-ch-ua-bitness>

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`Sec-CH-UA-Bitness`	93	93	No	79	No	93	No	66	No	23.0	93	No