**
*Contact emails*
*
miketa...@chromium.org, abe...@chromium.org, jadekess...@chromium.org
Explainer
https://github.com/WICG/ua-client-hints#explainer-reducing-user-agent-granularity
<https://github.com/WICG/ua-client-hints#explainer-reducing-user-agent-granularity>
Specification
https://www.chromium.org/updates/ua-reduction
<https://www.chromium.org/updates/ua-reduction>is the closest thing that
specifies Chrome’s UA Reduction plans today. As these changes land in
Chromium, the Compat Standard <https://compat.spec.whatwg.org/>will be
updated to reflect them (in the newly landed UA String section
<https://compat.spec.whatwg.org/#ua-string-section>).
Summary
As previously detailed on the Chromium Blog
<https://blog.chromium.org/2021/09/user-agent-reduction-origin-trial-and-dates.html>,
we intend to proceed with Phase 4 of the User-Agent Reduction plan.
In Phase 4, the MINOR.BUILD.PATCH version numbers are reduced to
"0.0.0". For use cases requiring high-entropy full version information,
developers are encouraged to migrate to the User Agent Client Hints API
<https://web.dev/migrate-to-ua-ch/>, in particular the
Sec-CH-UA-Full-Version-List
<https://wicg.github.io/ua-client-hints/#sec-ch-ua-full-version-list>hint.
Blink component
Blink <https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink>
TAG review
https://github.com/w3ctag/design-reviews/issues/640
<https://github.com/w3ctag/design-reviews/issues/640>
TAG review status
Issues addressed
Risks
Interoperability and Compatibility
Any time you modify the User-Agent string there is a risk of some
content somewhere depending on the previous format.
There should not be interop risks, as each browser sends its own
User-Agent string. But there is a risk that content somewhere is relying
on “non-zero” MINOR, BUILD, or PATCH information. My personal view is
that the risk is low compared to the rest of the changes to come in
later phases. But in order to mitigate the risk of this change, we
intend to slowly roll it out via Finch and observe health metrics (i.e.,
HTTP 4XX and 5XX error codes, etc.) and bug reports from the community.
We've surveyed dozens of User-Agent parsing libraries, and as far as we
know "0.0.0" will not create a problem syntactically. But the web can
get pretty weird in ways we don't anticipate, hence the slow roll-out
and incremental path towards User-Agent Reduction.
Gecko: Shipped/Shipping. Firefox has frozen (or capped) much of their UA
string already.
WebKit: Shipped/Shipping. Safari has already frozen everything in their
UA string except for version number info.
Web developers: Mixed signals. Reactions have ranged from positive to
indifferent to negative, from various channels.
Debuggability
No special DevTools support needed.
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>?
No
Flag name
reduce-user-agent
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1282229
<https://bugs.chromium.org/p/chromium/issues/detail?id=1282229>
Launch bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1282238
<https://bugs.chromium.org/p/chromium/issues/detail?id=1282238>
Estimated milestones
We aim to start rollout in M101. We will update this thread once the
feature is shipping to 100% of the stable population.
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/6311349754789888
<https://chromestatus.com/feature/6311349754789888>
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