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We are migrating the User-Agent Client Hint tokens from “ua-*” to “sec-ch-ua-*” . Our proposed timeline is to get this change merged to Chrome 88 (stable cut for which is on January 12th, rollout on Jan 19th), before the UA-CH feature is fully rolled out and usage is still low. This will require a fair amount of work; more on that below.


The current ACCEPT-CH tokens for client hints are in the format “ua-*”. This isn’t in line with Client Hints, Section 3.1, which recommends the tokens be the same as the associated header names. This should also hopefully reduce confusion for those that want to use the feature.


Specification link

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Status in Chromium


In development (tracking bug)

Consensus & Standardization

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Migration We believe it would be best to make a clean switch instead of supporting both formats of tokens for a number of releases because there’s little to no usage outside of testing, demos, and documentation, most of which is internal. We’re hoping to get all of this out into milestone 88, so we can get this changed before a full rollout is announced and people start actually using it. We are open to consider alternative opinions from API owners, however, if this does not seem like a reasonable course of action.

Last updated on 2021-09-10