As previously detailed in https://blog.chromium.org/2021/09/user-agent-reduction-origin-trial-and-dates.html, we intend to proceed with Phase 5 of the User-Agent Reduction plan. The <platform> and <oscpu> tokens (i.e., parts of the User-Agent string) are reduced to the relevant <unifiedPlatform> token values, and will no longer be updated. Additionally, the values for navigator.platform are frozen on desktop platforms (see https://www.chromium.org/updates/ua-reduction/#reduced-navigatorplatform-values-for-all-versions). This is phase 5 of the User-Agent reduction plan as described in https://blog.chromium.org/2021/09/user-agent-reduction-origin-trial-and-dates.html. For use cases requiring high-entropy OS version, CPU architecture, bitness or Wow64-ness, developers are encouraged to request that via the User Agent Client Hints API, in particular the Sec-CH-UA-Platform, Sec-CH-UA-Platform-Version, Sec-CH-UA-WoW64, Sec-CH-UA-Arch, and Sec-CH-UA-Bitness client hints.
As noted in the User Agent Client Hints explainer, the User Agent string presents challenges for two reasons. Firstly, it passively exposes quite a lot of information about the browser for every HTTP request that may be used for fingerprinting. Secondly, it has grown in length and complexity over the years and encourages error-prone string parsing. We believe the User Agent Client Hints API solves both of these problems in a more developer- and user-friendly manner.
Explainers: https://github.com/WICG/ua-client-hints#explainer-reducing-user-agent-granularity