v147 · Performance · Prerendering

Prerendering Cross-Origin iframe Opt-in Flow

Chrome 147 allows cross-origin iframes to participate in prerendering by sending Supports-Loading-Mode: credentialed-prerender. Walk through the opt-in flow for both the embedding page and the iframe origin.

Click "Next step" to walk through the flow.

live browser probe

the headers

# Speculative rules on the embedding page:
<script type="speculationrules">
{
  "prerender": [{ "source": "list", "urls": ["/next-page"] }]
}
</script>

# /next-page embeds cross-origin iframe:
<iframe src="https://partner.example.com/widget"></iframe>

# partner.example.com/widget response header (opt-in):
Supports-Loading-Mode: credentialed-prerender

# Without this header, Chrome defers the iframe load
# until the prerendered page activates.

references

implementation reference

Need the exact API surface, compatibility boundaries, errors, lifecycle, and source links? Read the matching gendn reference ↗