Intent to Ship: Prerendering cross-origin iframes

[Chromestatus]

Contact emails

yoi...@chromium.org

Explainer

https://github.com/WICG/nav-speculation/blob/main/prerendering-cross-origin-iframes.md

Specification

https://wicg.github.io/nav-speculation/prerendering.html

Summary

Prerenders cross-origin iframes with an opt-in response header. Browsers will now prerender all cross-origin frames if the top-level frame's HTTP response includes the Supports-Loading-Mode: prerender-cross-origin-frames.

Blink component

Blink

Web Feature ID

speculation-rules

Motivation

By default, navigational prerendering delays the loading of all cross-origin iframes until the referring page activates the prerendered page. However, there are some cases where cross-origin iframes are particularly important to an application, such that delaying them negates many of the benefits of prerendering.

Initial public proposal

https://groups.google.com/a/chromium.org/g/blink-dev/c/KP1f2UTqCgM/m/q_EQ5ceXHgAJ

TAG review

https://github.com/w3ctag/design-reviews/issues/1207

TAG review status

Issues addressed

Origin Trial Name

Prerendering cross-origin iframes

Goals for experimentation

Gather feedback from web authors who already are interested in this feature.

Chromium Trial Name

Prerender2CrossOriginIframes

Origin Trial documentation link

https://github.com/WICG/nav-speculation/blob/main/prerendering-cross-origin-iframes.md

WebFeature UseCounter name

kPrerender2CrossOriginIframes

Risks

Interoperability and Compatibility

The entire speculative loading feature is a progressive enhancement, so in general risks are low in this area.

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/1376) No signal as of 2026-10-15

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/636) No signal as of 2026-10-15

Web developers: Positive Our partners have given positive feedback on this feature.

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.

Debuggability

The cross-origin iframe prerendering should be debuggable as well as top frame's one: https://developer.chrome.com/docs/devtools/application/debugging-speculation-rules#prerender

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

No

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

Yes

Flag name on about://flags

"prerender2-cross-origin-iframes" from M148

Finch feature name

Prerender2CrossOriginIframes

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/440387014

Availability expectation

Feature is available only in Chromium browsers for the foreseeable future.

Adoption expectation

Feature is used by specific partner(s) to provide functionality within 12 months of launch in Chrome.

Adoption plan

One of our partners has already joined in origin trial in Chrome and shows better performance result.

Non-OSS dependencies

Does the feature depend on any code or APIs outside the Chromium open source repository and its open-source dependencies to function?

No.

Estimated milestones

Shipping on desktop	158
Origin trial desktop first	147
Origin trial desktop last	152
Origin trial extension 1 end milestone	158
Shipping on Android	158
Shipping on WebView	158
Shipping on iOS	158

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 information provided

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5112398709129216?gate=5121426126405632

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68b670ba.050a0220.270bc4.0593.GAE%40google.com
Intent to Experiment: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAAEV3p%3DzhNhfOpe8x%3DRKgxYFS9GCq_q-c8knZYRBRuijQ27o8w%40mail.gmail.com
Intent to Extend Experiment 1: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a45fcf5.198129d7.1d0cd0.0014.GAE%40google.com

This intent message was generated by Chrome Platform Status.

[Alex Russell]

Do we have a sense for which sorts of applications will benefit from this change? This Intent mentions an OT; was there feedback from developers about the utility of x-origin iframe pre-rendering? Did we learn anything about the potential risks (e.g., to metrics and privacy)?

Thanks,

Alex

[Yoichi Osato]

> This Intent mentions an OT; was there feedback from developers about the utility of x-origin iframe pre-rendering?

Yes, one of our customers shows significant performance improvement(68%!) on speculative loading with this feature.

> Did we learn anything about the potential risks (e.g., to metrics and privacy)?

No report from OT attendees so far.

2026年10月22日(木) 0:24 Alex Russell <sligh...@chromium.org>:

[Alex Russell]

Thanks for the data. It's exciting to hear about such a large performance improvement. 

LGTM1

Not blocking, but just curious: it would be unfortunate if the major customers of this API were ad systems. Do we have good data from non-ads use-cases?

Best,

Alex

[Mike Taylor]

LGTM2

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.
To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/711e83ed-5e6d-4b36-ae28-5c4d04a6a568n%40chromium.org.

[Chris Harrelson]

LGTM3

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/0c665826-82e5-4c57-9f0e-8688b3421c5a%40chromium.org.

[Yoichi Osato]

>  it would be unfortunate if the major customers of this API were ad systems. Do we have good data from non-ads use-cases?

The customer actually tested this feature on non-Ads use case:)

2026年10月28日(水) 3:51 Alex Russell <sligh...@chromium.org>:

[Yoichi Osato]

FYI: Due to some additional implementation work, this feature missed the M158 branch cut.

The flag flip has landed for M159 (or whichever milestone it landed in), and ChromeStatus has been updated accordingly.

2026年10月28日(水) 14:54 Yoichi Osato <yoi...@chromium.org>: