Shopify Checkout Extensibility Explained

Who it is for

Store owners and developers after the upgrade

Time needed

1 to 2 hours to audit

What you need

Admin access and your analytics

For years, customizing Shopify's checkout meant one of three things: editing checkout.liquid on Plus, pasting code into the additional scripts box, or writing Ruby in the Script Editor. All three are gone. What replaced them is called checkout extensibility, and most of the confusion I see comes from treating it as one feature. It's a toolkit, and each tool has its own job and its own plan rules.

This guide explains each part in plain terms, the deadlines that forced stores to move, what makes an app "checkout extensibility compatible", and how to rebuild Google Tag Manager tracking. Dates and plan rules were checked on shopify.dev and the Shopify Help Center on 7 November 2026.

What is Shopify checkout extensibility?

Checkout extensibility is Shopify's way of letting apps and developers change checkout without touching its code. Instead of editing a template, you add pieces that Shopify hosts and runs in defined places. Shopify describes the result as upgrade-safe: when Shopify improves checkout, your customizations keep working, and Shop Pay, express payments and new checkout features stay available.

The trade-off is control. You can't move the payment button or rewrite the page. You can add blocks where Shopify allows them, change logic through functions, style within the branding options, and track through pixels.

The parts of checkout extensibility

Two plan rules cause most of the surprises. First, checkout UI extensions on the information, shipping and payment steps are Plus only, while the thank you and order status pages are available from Basic up. Second, custom apps that contain Shopify Functions only work on Plus. Public App Store apps with functions work on any plan.

The deadlines that moved every store

checkout.liquid is now unsupported for the information, shipping and payment steps. The thank you and order status pages followed in two stages, and Scripts were retired separately:

If your store was upgraded automatically, the risk isn't that checkout broke. It's that something stopped quietly: a conversion pixel in additional scripts, a script-based discount, a custom message on the thank you page. I cover how to audit that below.

What a "checkout extensibility app" is

An app is compatible with checkout extensibility when it customizes checkout through these official surfaces: a checkout UI extension, a function, a web pixel or the Branding API. Older apps that injected script tags into the thank you page no longer work there.

To see what an installed app actually adds:

1. Open the app's page. Go to Settings > Apps and click the app's name.
2. Check extensions and functions. The app's page lists its extensions and functions, and its pixel status.
3. Check where blocks can go. In the checkout and accounts editor, open the Apps sidebar and click the plus icon next to a block to see which pages it supports.
4. Check the plan. If a block only supports the information, shipping or payment steps, it needs Plus.

Before buying any checkout app on a non-Plus store, I ask the developer one question: which pages does this work on below Plus? Many listings show in-checkout screenshots that only apply to Plus stores.

Shopify checkout extensibility and GTM

Google Tag Manager can't sit in checkout's HTML any more. It runs inside a custom pixel, in a sandbox, and receives Shopify's standard events. Shopify's Help Center has a tutorial for this; the steps I follow are:

1. Remove old GTM code. Delete GTM and duplicate tracking from theme.liquid and anywhere else it was pasted, so events aren't counted twice.
2. Create the pixel. Go to Settings > Customer events, enter a name and click Add pixel.
3. Set privacy. In Customer privacy, choose whether the pixel needs customer permission and for which purposes.
4. Paste the GTM snippet. Copy GTM's head snippet, remove the <script> tags and paste the JavaScript into the code window.
5. Subscribe to events. Push each Shopify event you need into the data layer.
6. Save and connect. Click Save, then Connect pixel.
7. Build the GTM side. In GTM, create custom event triggers with the same event names, and at least one tag. Shopify notes data won't flow without a tag and trigger.

The event subscription for a purchase looks like this:

analytics.subscribe("checkout_completed", (event) => {
  window.dataLayer.push({
    event: "checkout_completed",
    orderId: event.data?.checkout?.order?.id,
    value: event.data?.checkout?.totalPrice?.amount,
    currency: event.data?.checkout?.currencyCode
  });
});

The checkout events available are checkout_started, checkout_contact_info_submitted, checkout_address_info_submitted, checkout_shipping_info_submitted, payment_info_submitted and checkout_completed, alongside storefront events such as product_viewed and product_added_to_cart.

Where possible, I use the official app pixels from Google and Meta channels for standard conversion tracking, and keep a GTM custom pixel only for tags that have no app. Fewer tags in the sandbox means fewer things to break.

How developers build a checkout UI extension

1. Generate it. Inside an app, run shopify app generate extension --template checkout_ui.
2. Pick targets. A block target such as purchase.checkout.block.render lets merchants place the block in checkout. purchase.thank-you.block.render targets the thank you page, which works on every plan.
3. Build the UI. Extensions use Shopify's Polaris web components, with Preact in the templates. You can't inject arbitrary HTML or CSS, which is what keeps checkout consistent.
4. Keep it small. The compiled bundle can't exceed 64 KB.
5. Preview and deploy. shopify app dev previews on a development store, and shopify app deploy releases it.
6. Place it. The merchant adds the block in the checkout and accounts editor.

For logic rather than UI, such as hiding a delivery option, the right tool is a function. My Shopify Functions guide covers those.

How to audit a store after the upgrade

1. List what the old checkout did. Check old theme backups, your additional scripts history if you saved it, and any Script Editor notes.
2. Check tracking. Compare orders in Shopify with purchases recorded in GA4 and ad platforms for the same week. A big gap means a pixel is missing.
3. Check discounts. Any discount that depended on Scripts stopped on 30 June 2026. Rebuild it with native discounts or a function-based app.
4. Check post-purchase content. Surveys, upsells and messages on the thank you page need app blocks now.
5. Check apps. Remove apps that only worked through old script tags.

Common mistakes

1. Assuming auto-upgrade meant nothing changed. Tracking and script discounts are the usual casualties.
2. Leaving GTM in the theme and adding a pixel. Storefront events then fire twice.
3. Buying Plus-only checkout apps on Grow or Advanced.
4. Ignoring consent settings on custom pixels in regions that need permission.
5. Testing GTM with tools that don't support the sandbox.

Checkout extensibility checklist

Next steps

Open Settings > Customer events and Settings > Apps today and write down what's connected. Then compare last week's orders with the purchases your analytics recorded. If the numbers match and your discounts work, the move is done. If not, the gap tells you where to look.

For hands-on changes, my guide on how to customize your Shopify checkout has the admin steps. If you need a checkout extension or pixel built, my app development service starts from $800.

Frequently asked questions

Sources

1. Checkout apps overview, Shopify.dev
2. Checkout UI extensions, Shopify.dev
3. Upgrading your Thank you and Order status pages, Shopify Help Center
4. Create a Google Tag Manager custom pixel, Shopify Help Center
5. Managing custom pixels, Shopify Help Center
6. Web Pixels API, Shopify.dev

Related services and work

Written by Ashraf Siddik

I'm a Shopify developer and CRO specialist. I have built and improved Shopify stores since 2018, completed more than 1,000 projects, and hold a 4.96 average rating across 719 client reviews.

About me · Client reviews