Intent to Extend Experiment: User-Agent Reduction Deprecation Origin Trial

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Ari Chivukula

May 19, 2023, 12:02:38 PM5/19/23
to Ari Chivukula, Victor Tan, Mike Taylor, blink-dev

Contact emails,,

Original I2E

Origin Trial Overview

Client Hints Infrastructure Spec

Origin Trial


We propose extending the User-Agent Reduction Deprecation origin trial, which allows developers to continue to receive the full User-Agent string. We decided to extend the experiment based on ecosystem feedback and a bug that was identified in the implementation of the origin trial for user agent reduction and user agent reduction deprecation.  We are planning to extend the end date from March 23, 2023 (M112) to August 8, 2023 (M115). We are in the process of resolving the bug and the information can be found here.

Blink component



We received feedback from the ecosystem that it would be helpful to extend the origin trial. The User-Agent Reduction for Phase 6 just reached 100% on May 12th and this gives additional time to evaluate the impact of those changes. In addition, this bug may have impacted the ability of developers to prepare their sites for the end of the Deprecation Trial, and so  extending the Deprecation Trial to fix the bug in M115 ensures additional ecosystem support.

TAG review (resolved w/ concerns)


The risks are minimal here; this just extends the ability to send the legacy User-Agent header for 3 additional milestones.


DevTools supports debugging HTTP headers, so no special tooling is needed.

Is this feature fully tested by web-platform-tests?

Tests will be added once the bug is resolved to verify.

Tracking bug

Link to entry on the Chrome Platform Status

Rick Byers

May 19, 2023, 1:40:29 PM5/19/23
to Ari Chivukula, Victor Tan, Mike Taylor, blink-dev
LGTM. Deprecation trials are very low risk from an interoperability perspective, I don't have any concern with doing an extension given the context of the bug etc.

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Ari Chivukula

May 19, 2023, 3:38:51 PM5/19/23
to Rick Byers, Victor Tan, Mike Taylor, blink-dev
The extension was approved until September 23, 2023. It looks like that's the standard final date for OTs that support M115.
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