Intent to Ship: Long Animation Frames style and layout duration

[Yoav Weiss (@Shopify)]

Contact emails

yoav...@chromium.org

Explainer

https://github.com/w3c/long-animation-frames/pull/30#issue-3828859369

Specification

https://github.com/w3c/long-animation-frames/pull/30

Summary

Add `styleDuration` and `forcedStyleDuration` information to the Long Animation Frame API, enabling developers to distinguish style and layout times.

Blink component

Blink>PerformanceAPIs

Web Feature ID

Missing feature - https://github.com/web-platform-dx/web-features/issues/4453

Motivation

Currently performance-conscious developers have no way to distinguish their style time from their layout time, making CSS performance issues less actionable than they can be. This feature enables developers to make that distinction.

Initial public proposal

https://github.com/w3c/long-animation-frames/pull/30

TAG review

I didn't file for a TAG review as these are a few new attributes that break up the timings provided by an existing attribute, mimicking its existing shape. I don't expect the TAG to have strong opinions on the shape of the attributes.

TAG review status

Not applicable

Origin Trial Name

Long Animation Frames - separate style and layout durations

Goals for experimentation

See that the new attributes provide useful data to developers as they debug their CSS performance issues.

Chromium Trial Name

LongAnimationFrameStyleDuration

Link to origin trial feedback summary

https://groups.google.com/a/chromium.org/g/blink-dev/c/qvGqBcSOFTQ/m/rU6rqKuMCAAJ

Origin Trial documentation link

https://github.com/w3c/long-animation-frames/pull/30#issue-3828859369

WebFeature UseCounter name

kLongAnimationFrameTimingStyleDuration

Risks

Interoperability and Compatibility

As these are new attributes, I don't expect them to have any compat impact. As far as interop goes, I'd expect that when other engines adopt LoAF, they'd also adopt these attributes.

Gecko: No signal 
Positive on the broader LoAF: https://github.com/mozilla/standards-positions/issues/929
I'm asking if I should file a more specific issue for these extra attributes.

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/283) 
No signal for the broader LoAF feature. Unlikely they'd have a strong position on these attributes.

Web developers: Positive (https://groups.google.com/a/chromium.org/g/blink-dev/c/qvGqBcSOFTQ/m/5DCTOu9KCgAJ)

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Debuggability

No information provided

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

Yes

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

Yes

 - https://wpt.fyi/results/long-animation-frame/loaf-style-duration.html: styleDuration (9 subtests)
 - https://wpt.fyi/results/long-animation-frame/loaf-layout-duration.html: layoutDuration (7 subtests)
 - https://wpt.fyi/results/long-animation-frame/loaf-forced-style-duration.html: forcedStyleDuration (4 subtests)
 - https://wpt.fyi/results/long-animation-frame/loaf-forced-layout-duration.html: forcedLayoutDuration, including checking that forced style plus forced layout
   adds up to forcedStyleAndLayoutDuration (5 subtests)
 - https://wpt.fyi/results/long-animation-frame/loaf-container-queries.html: all four attributes when container queries mix style and layout work (6 subtests)
 - https://wpt.fyi/results/long-animation-frame/loaf-toJSON.html: now also checks styleDuration and layoutDuration in toJSON()

Flag name on about://flags

No information provided

Finch feature name

LongAnimationFrameStyleDuration

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/476826067

Estimated milestones

Shipping on desktop	157
Origin trial desktop first	148
Origin trial desktop last	153
Shipping on Android	157
Shipping on WebView	157

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

No changes expected.

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5171478175809536?gate=6516503656660992

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOmohSJxRuMp6Ha5RVCjzNfsG0Sj96Y%3Dgy9LnxtM%2Brq-S6DEew%40mail.gmail.com
Intent to Experiment: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOmohSJ2PJ0dZxYH48PALOSUenSSV7VuZ9CzTHnGd8u_jTKkcg%40mail.gmail.com

This intent message was generated by Chrome Platform Status.

[Alex Russell]

LGTM1; this is an awesome addition. Thanks for making it happen.

On TAG review, can you please send an FYI?

Best,

Alex

[Rick Byers]

Looks good to me, but is there any reason this PR can't land now?

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[Yoav Weiss (@Shopify)]

On Wednesday, October 7, 2026 at 6:18:53 PM UTC+3 Rick Byers wrote:

Looks good to me, but is there any reason this PR can't land now?

It needed some more work. It has landed now.

 

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[Philip Jägenstedt]

LGTM2

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[Philip Jägenstedt]

Can you take care of the Security gate in chromestatus.com so that the last API owner approver does not need to bypass that?

[Mike Taylor]

LGTM3 (I see security is approved now)

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