Intent to Extend Origin Trial: Early Hints preload/preconnect during Navigation

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Kenichi Ishibashi

Oct 7, 2021, 2:39:38 AM10/7/21
to blink-dev, Yutaka Hirano, Daisuke Enomoto

We would like to extend Early Hints preload/preconnect Origin Trial to M98 (originally planned to end in M96).

Contact emails



Design docs


Support 103 Early Hints informational responses for navigation. When a 103 response includes <link rel=preload> or other link headers Chromium tries to preload (and/or preconnect, prefetch) specified resources even before the final response is received. This gives Web developers a way to optimize Core Web Vitals such as Largest Contentful Paint (LCP).

Blink component


TAG review

TAG review status



Interoperability and Compatibility

Several servers/proxies may not understand a 103 response. They may treat the 103 response as a part of the final response when the response is sent over HTTP/1.1. The problem is less likely to happen over HTTP/2 thanks to their frame format. Chromium only handles 103 responses over HTTP/2 and HTTP/3.

Gecko: Worth prototyping (

WebKit: No signal (

Web developers: Positive ( Web developers: Positive ( Positive interest and intent of support by popular CDNs. We've been collaborating with Fastly to do the preliminary measurement.

Goals for experimentation

Allows web developers to opt-in Early Hints preloads. We use custom page load metrics (FCP, LCP FID) to measure performance impact.

Reason this experiment is being extended

We added preconnect support in M95 based on Web developer's feedback and we are now evaluating the impact of preload and preconnect. We realized that we need more time to evaluate the impact of this feature. We have partners lined up for the feature and we expect to get more data in coming months.

Ongoing technical constraints



If a resource is preloaded by Early Hints, the corresponding PerformanceResourceTiming object reports initiatorType is "early-hints". For more details, see

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?


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


Flag name


Requires code in //chrome?


Tracking bug

Launch bug

Estimated milestones

OriginTrial desktop last95 → 98
OriginTrial desktop first94
OriginTrial android last95 → 98
OriginTrial android first94

Link to entry on the Chrome Platform Status

Links to previous Intent discussions

Intent to Experiment:

This intent message was generated by Chrome Platform Status.

Yoav Weiss

Oct 7, 2021, 3:27:18 AM10/7/21
to Kenichi Ishibashi, blink-dev, Yutaka Hirano, Daisuke Enomoto
LGTM to extend to M98. 5 milestones overall seems reasonable.

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Anne van Kesteren

Nov 2, 2021, 4:47:14 AM11/2/21
to Kenichi Ishibashi, blink-dev, Yutaka Hirano, Daisuke Enomoto
On Thu, Oct 7, 2021 at 8:39 AM Kenichi Ishibashi <> wrote:
> Specification

When do you expect to make progress on The RFC doesn't fully
define this feature.

Kenichi Ishibashi

Nov 3, 2021, 6:54:08 PM11/3/21
to Anne van Kesteren, blink-dev, Yutaka Hirano, Daisuke Enomoto
Hi Anne,

We plan to start working on the spec issue in this quarter.


Anne van Kesteren

Nov 4, 2021, 5:27:31 AM11/4/21
to Kenichi Ishibashi, blink-dev, Yutaka Hirano, Daisuke Enomoto
On Wed, Nov 3, 2021 at 11:54 PM Kenichi Ishibashi <> wrote:
> We plan to start working on the spec issue in this quarter.

That's great to hear, appreciate the update!
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