What Are User-Agent Client Hints

The browser industry recognized that the User-Agent string is so detailed that it's abused for user tracking (fingerprinting). What emerged as the alternative is User-Agent Client Hints (UA-CH).

What Changes

UA-CH splits information such as browser, platform, and mobile status into separate HTTP headers, and lets the server request only the information it needs. The low-entropy hints exposed by default are as follows.

• Sec-CH-UA — the browser brand and major version
• Sec-CH-UA-Mobile — mobile status (?0 / ?1)
• Sec-CH-UA-Platform — the operating system name

High-Entropy Hints

Detailed information such as the exact OS version, device model, and architecture can only be received if the server explicitly requests it. This reduces the information exposed by default and obtains details only when needed.

Will the Existing UA Disappear

It won't disappear right away. Chromium-based browsers are gradually changing toward freezing the detailed version in the UA string (reduced UA), and in JavaScript you can access UA-CH via navigator.userAgentData.

For server log analysis and statistics, it's safest to consider both the UA string and UA-CH together for the time being.