Instant Embed is a Shopify app embed that loads Instant's scripts on your live storefront. Your layouts work either way — enabling it makes Instant pages and sections faster.
When you click Publish, Instant checks whether the app embed is enabled. If it isn't, a modal prompts you to enable it first.
Prerequisites
Your Shopify store connected to Instant (status: Connected).
Permission to edit your Shopify theme.
Enable Instant Embed while publishing
In the builder, click Publish on a layout.
If the embed isn't enabled, the Enable app embed in Shopify modal appears.
Click Enable in Shopify. This opens your Shopify theme editor with the Instant app embed ready to activate.
Confirm the app embed toggle is on, then click Save in the Shopify theme editor.
Return to Instant. The modal now shows a Welcome back! step — click Verify & Publish.
Instant confirms the embed is active and continues publishing.
Skip and publish
The modal also offers Skip & Publish. Your layouts still go live and still work; your storefront just loads more slowly until the embed is on.
Tips
Enable Instant Embed on the theme you actually publish to (set in Settings → Shopify).
If you switch to a new Shopify theme, enable the embed on that theme too.
Troubleshooting
Instant shows "App embed not enabled" after I turned it on
Make sure you clicked Save in the Shopify theme editor after toggling the app embed on.
Confirm you enabled the embed on the same theme Instant publishes to (Settings → Shopify).
Click Verify & Publish again in Instant.
"Enable in Shopify" opens the wrong theme
Set the correct theme in Settings → Shopify, then try publishing again.
See also How publishing works.