Shopify Checkout Extensibility in 2026: What Store Owners Need to Know

Shopify Checkout Extensibility is the supported way to customize Shopify checkout: checkout UI extensions, Shopify Functions, web pixels and branding settings replace checkout.liquid, Additional Scripts and Shopify Scripts. By October 2026 every legacy method has reached its end date: checkout.liquid is unsupported on all checkout pages, the Thank you and Order status upgrade deadlines have passed for every plan, and Shopify Scripts stopped running on June 30, 2026.

So the question for 2026 is no longer whether to migrate. It is whether your checkout still works the way your business needs: tracking that reports every order, apps that behave, post-purchase pages that are complete, and business rules that were rebuilt rather than lost. This guide covers the tools, the dates, what each plan can do and what to check.

What is Shopify Checkout Extensibility?

Checkout Extensibility is the set of tools Shopify provides for changing checkout without editing its code. In its developer docs, Shopify now also calls it "Shopify Extensions in Checkout". Instead of editing a template, you place apps and extensions at fixed points in checkout and run your business logic as Functions on Shopify's servers. Customizations built this way keep working when Shopify updates checkout.

What changed, and when?

These are the dates that matter, checked against shopify.dev, the Shopify Help Center and the Shopify changelog.

If your store still shows an old Thank you or Order status page, upgrade it now. Shopify's help center gives the deadline but does not say what happens to stores that missed it.

What replaces checkout.liquid, Additional Scripts and Shopify Scripts?

Every old customization has a supported replacement, but not always a one-click one. Simple changes move to settings or an app. Complex logic usually needs development work.

How do the main tools work?

Checkout UI extensions

• Extensions render at fixed places in checkout called targets. Merchants place block extensions in the checkout and accounts editor.
• They are built with Shopify's Polaris web components, and Shopify recommends Preact. API version 2025-07 was the last to support the older React components. To keep deploying after October 1, 2026, an extension must use API version 2026-01 or later.
• The JavaScript bundle is limited to 64 KB compressed.
• Extensions can't override CSS, can't reach the real checkout DOM and can't render arbitrary HTML. Checkout always uses the merchant's own branding, which is why styling goes through branding settings instead.
• Calls to your own server need the network access capability, and the server must allow cross-origin requests.
• For validation, Shopify now recommends the Cart and Checkout Validation Function over a blocking UI extension, because Functions are guaranteed to run.

Shopify Functions

Functions run your logic on Shopify's infrastructure during cart and checkout. In API version 2026-10 the Function APIs include:

• Discount. One API for product, order and shipping discounts since version 2025-04.
• Delivery Customization. Hide, rename or reorder shipping options.
• Payment Customization. Hide, rename or reorder payment methods.
• Cart and Checkout Validation. Block checkout when rules are broken, such as quantity limits or B2B minimums. We cover it in detail in custom checkout validation with Shopify Functions.
• Cart Transform. Bundles and line item changes.
• Fulfillment Constraints and Order Routing. Control where and how orders are fulfilled. Order routing is a beta available on request to Plus merchants.
• Local pickup and pickup point delivery option generators. Custom pickup options.

Shopify's rule on plans is short. Stores on any plan can use public App Store apps that contain Functions. Only Shopify Plus stores can use custom apps that contain Functions, and a few capabilities are Plus-only.

Web pixels and customer events

Tracking that used to live in Additional Scripts now runs through customer events. Add a custom pixel under Settings > Customer events, or install an app pixel from your analytics or ad provider. Custom pixels run in a sandboxed iframe, and app pixels run in a stricter sandbox in a web worker. Neither has direct access to the checkout page.

Checkout tracking uses Shopify's standard events, including checkout_started, checkout_contact_info_submitted, checkout_address_info_submitted, checkout_shipping_info_submitted, payment_info_submitted and checkout_completed.

Branding

Every store on Basic or higher can set the logo, colors, fonts and background in the checkout and accounts editor. Plus stores can go further through the GraphQL Admin API. The older checkoutBrandingUpsert mutation is now marked deprecated in favor of checkoutAndAccountsConfigurationUpdate, released in May 2026, which also covers customer accounts. Shopify says the old mutation is still supported.

Post-purchase extensions and Checkout Blocks

Post-purchase extensions show an offer after payment and before the Thank you page. They are still in beta, and using one on a live store requires an access request. Stores on any plan except Starter can install App Store apps that use them, while custom post-purchase apps are Plus-only.

Checkout Blocks is Shopify's own app. On Plus, it adds content blocks, custom discounts, order value limits, and rules that hide, rename or reorder shipping and payment methods, all without code. On other plans it offers content blocks on the Thank you and Order status pages, and, since April 2026, order value limits.

Plus vs non-Plus: what can each plan customize?

Shopify's documentation excludes the Starter plan from most of these features. checkout.liquid was only ever available on Plus, and it is now unsupported everywhere.

What should store owners review in 2026?

Start with the checkout customizations report in your admin under Settings > Checkout. Shopify generates it automatically and sorts your old Additional Scripts by purpose, such as order tracking. Then go through the areas below. This doesn't need to be a huge technical audit, but it should be more than clicking "upgrade" and hoping for the best.

Thank you and Order status pages

These pages sit right after purchase and often carry conversion pixels, surveys, upsells, delivery information and support links. Check that each one still shows the right information and that the page still gives customers a clear next step.

Tracking, pixels and apps

Tracking is the area most likely to break quietly. Place test orders and compare purchases in Shopify with GA4, Meta, Google Ads and any affiliate platform. This matters most for stores that rely on paid ads, affiliate payouts or email flows triggered by purchases.

Custom checkout logic

Some rules are invisible from the front end: payment or shipping conditions, B2B rules, special discounts and fraud checks. If any of them ran on Shopify Scripts, they stopped on June 30, 2026. Confirm that each one was rebuilt as a Function or an app, and that the business rule behind it still works, not just that checkout looks fine.

App and extension versions

Ask your app vendors whether their checkout extensions are on API version 2026-01 or later. If you have your own custom app with checkout extensions, update it, because extensions on older versions can no longer be deployed after October 1, 2026.

Customer accounts

Legacy customer accounts are deprecated. If your store still uses them, plan the move to new customer accounts before Shopify announces the final sunset date, and check any Order status page customizations along the way.

How do you migrate an old customization?

1. Export what exists. Use the customizations report and back up any old scripts and checkout code you still have.
2. Write down the purpose of each item. For example, "fires the Meta purchase event", "hides cash on delivery for orders over €500" or "adds a delivery date field".
3. Choose a replacement for each. A built-in setting, an App Store app, a custom app (UI extension, Function or pixel), or nothing if nobody needs it anymore.
4. Build and test on a development store. Test on mobile, with different payment methods, discounts and markets.
5. Check tracking with real test orders. Compare event counts in every analytics and ad platform with Shopify orders.
6. Publish and monitor. Watch conversion rate, checkout errors and app reports closely for the first two weeks.

How does it affect UX and conversion?

Checkout Extensibility is a technical change, but its effect on customers is not only technical. Small changes in layout, payment options, shipping choices, trust signals or post-purchase messages can change conversion.

After the technical work, review checkout from the customer's side. Is it clear on mobile? Are payment and shipping options easy to understand? Are important trust signals still visible? Does the Thank you page offer the right next step? A checkout that is upgraded but harder to use is not a successful upgrade.

When do you need a developer?

Not every store does. If you use standard payment methods, simple tracking and a few common apps, branding settings, app pixels and App Store apps usually cover it.

You probably need a developer if checkout depends on custom logic, advanced tracking, B2B workflows, special discount rules, custom shipping or payment conditions, or integrations with systems outside Shopify. Old checkout scripts often have to become custom Shopify app development work, because custom apps can combine Functions, UI extensions and pixels in one place.

On Plus stores, checkout usually supports more than a basic purchase flow, so treat it as part of your wider Shopify Plus development rather than a quick settings change. Our Shopify Plus checkout customization service rebuilds checkout logic, tracking and post-purchase pages on the supported tools.

FAQ

Is checkout.liquid deprecated?

Yes. checkout.liquid is unsupported on the Information, Shipping and Payment steps, and it was sunset on the Thank you and Order status pages on August 28, 2025. It was only ever available on Shopify Plus. Its replacements are branding settings, checkout UI extensions, Shopify Functions and web pixels.

What was the deadline for non-Plus Shopify stores?

August 26, 2026 was the deadline for non-Plus stores to upgrade their Thank you and Order status pages. Additional Scripts have been view-only since August 28, 2025. If your store hasn't upgraded yet, do it now and move tracking to customer events.

Do Shopify Scripts still work?

No. Editing and publishing stopped on April 15, 2026, and all Shopify Scripts stopped running on June 30, 2026. Their logic now belongs in Shopify Functions, such as the Discount, Delivery Customization and Payment Customization APIs, or in Checkout Blocks on Plus.

What replaces Additional Scripts?

For tracking, custom pixels and app pixels under Settings > Customer events. For content on the Thank you and Order status pages, apps or checkout UI extensions. The right choice depends on what each script did, which the checkout customizations report helps you find out.

Do I need Shopify Plus for Checkout Extensibility?

Not for everything. All plans from Basic up get branding in the editor, Thank you and Order status extensions, web pixels and Functions from App Store apps. Plus adds extensions on the Information, Shipping and Payment steps, branding through the API and Functions in custom apps.

Do you need a developer for Checkout Extensibility?

Not always. Stores with standard settings can often use built-in tools and apps. If your store uses custom checkout logic, advanced tracking, B2B workflows, app-based conditions or integrations outside Shopify, have a developer review the setup before and after any change.