Shopify Checkout Extensibility in 2026: What You Can Customize Now

As of October 2026, there is only one way to customize Shopify's checkout: the app- and settings-based system Shopify calls Checkout Extensibility, which its developer docs now also describe as Shopify Extensions in Checkout. The old methods are gone. checkout.liquid no longer works on any checkout page, the Additional scripts box is view-only, and Shopify Scripts stopped executing on 30 June 2026.

What replaced them is a set of building blocks: checkout UI extensions for adding content, Shopify Functions for changing backend logic like discounts and shipping options, the checkout and accounts editor and Branding API for look and feel, and web pixels for tracking. Each one runs in a sandbox that Shopify controls, which is why Shopify calls these customizations upgrade-safe.

How much you can change depends on your plan. Every plan can brand the checkout and add apps to the Thank you and Order status pages. Only Shopify Plus can place app blocks on the information, shipping and payment steps or use the Checkout Branding API. Functions delivered through public App Store apps work on any plan.

This guide covers the timeline, what each piece does, what Plus and non-Plus stores can customize, and what to check now that the Thank you and Order status upgrade deadline has passed. It is part of our Shopify resource hub.

The timeline: how the old checkout was retired

Shopify's upgrade page now reads: "August 26, 2026 was the deadline to upgrade and replace your Thank you and Order status pages. Stores that weren't upgraded by that date were upgraded automatically." If your store was auto-upgraded, any tracking or content that depended on the old pages has stopped working, even if nobody noticed. That is the first thing to audit.

A related change affects the storefront rather than checkout: since 1 October 2026, apps can't create or update storefront script tags, and Shopify will stop injecting them on 1 March 2027.

What Checkout Extensibility is made of

Shopify's developer documentation lists four types of extensions for checkout: UI extensions, Functions, web pixel extensions and payments extensions. Merchants add most of them by installing apps and placing blocks in the checkout and accounts editor, without touching code.

Checkout UI extensions

UI extensions add content and inputs to checkout: upsell offers, custom fields (gift messages, delivery instructions), trust banners, surveys on the Thank you page or download links for digital goods. They are rendered by Shopify using its own components, so they inherit your checkout branding and can't break the page layout. Since API version 2025-10 they are built with Preact and Polaris web components and must stay under a 64 KB compiled bundle. Since January 2026 they are non-blocking by default, meaning an extension can't stop a buyer from progressing unless the merchant opts in.

Shopify Functions

Functions change backend logic: new discount types, hiding or reordering payment methods, renaming or hiding delivery options, cart and checkout validation, bundles and fulfillment rules. They are what replaced Shopify Scripts. We cover them in detail in a separate guide to Shopify Functions.

Branding

Branding covers the look of checkout and customer accounts: logo, colors, fonts and the order summary background. Every plan can set these in the checkout and accounts editor. Plus can go further with the Checkout Branding API and the Checkout Blocks app.

Web pixels

Web pixels are the supported way to track checkout events such as checkout started, payment info submitted and purchase. Apps install app pixels, and you can add custom pixels yourself in the admin. They replace the tracking snippets merchants used to paste into Additional scripts. Our guide to GA4 conversion tracking covers how to validate purchase events after the switch.

What non-Plus stores can customize

Shopify's checkout customization page says standard checkout customizations are available on all pages for businesses on the Basic plan or higher, and advanced features are Plus-only.

In practice, a non-Plus store can match its brand, add post-purchase content and surveys on the Thank you page, show order tracking or reorder prompts on the Order status page, and change discount, payment and delivery logic with Function-based apps. What it can't do is add upsells or custom fields inside the main checkout steps. One more recent limit applies to everyone: since 5 February 2026 you can no longer add a background image to the checkout header or main content area.

What Shopify Plus adds

Plus unlocks app blocks on every step of checkout, which is where the higher-impact customizations live: pre-purchase upsells next to the order summary, custom fields for delivery dates or gift options, loyalty point redemption and B2B fields like PO references. Plus stores can also use custom apps that contain Functions, so a developer can build store-specific logic without publishing a public app, and can request network access for some Function APIs.

The Checkout Branding API gives Plus stores finer control over styling than the editor exposes, and developers can combine it with UI extensions to customize the checkout header and footer. Combined with per-market checkout blocks, it lets a Plus store run noticeably different checkouts for different regions. Our Shopify Plus guide covers whether that is worth the plan cost.

The Thank you and Order status upgrade: what to check now

Because non-upgraded stores were switched automatically, many stores now have a new Thank you page that silently dropped old customizations. Shopify's guidance is to use blocks and web pixels to recreate them. Run through this list:

1. Place a real test order and confirm your analytics and ad platforms record the purchase once, with the right value. Missing or doubled purchase events are the most common post-upgrade problem.
2. Open Settings, then Checkout, and review the view-only Additional scripts box. Anything in it no longer runs; list what each snippet did.
3. Rebuild tracking with app pixels from your analytics and ad partners, or with a custom pixel. Shopify publishes a help page on replacing Google Tag Manager scripts on the Thank you page.
4. Rebuild visible content (surveys, social links, upsells, delivery estimates) with apps that offer Thank you or Order status blocks.
5. If you are on Plus and used checkout.liquid for anything on the main steps, confirm each customization has an extension or Function equivalent.

Replacing Shopify Scripts

Shopify Scripts were Ruby snippets that Plus stores used for line-item discounts, shipping rate changes and payment method rules. According to Shopify's Help Center, "As of June 30, 2026, Shopify Scripts has been deprecated. Any Scripts that were still published on your store have been deactivated and no longer work." The admin includes a Shopify Scripts customizations report (Apps, then Script Editor) that lists what was active and suggests Function-based apps or Function APIs to recreate each one.

Most common Script use cases now map to native features or Functions: tiered and bundle discounts to discount Functions or native discounts, hiding a payment method for certain carts to payment customization Functions, and renaming or hiding shipping rates to delivery customization Functions. For a broader comparison, see Shopify apps vs Shopify Functions.

Conversion: change less, test more

Extensibility limits what you can break, but it doesn't stop you adding clutter. Every block you place in checkout competes with the pay button. Add one change at a time, measure completion rate before and after, and remove blocks that don't earn their space. Our checkout optimization guide covers what usually moves conversion.

Conclusion

Shopify's checkout is now fully extension-based. Every plan can brand checkout, customize the Thank you and Order status pages with apps, track events with web pixels and use Function-based apps for discount, payment and delivery logic. Plus adds blocks inside the main checkout steps, custom Functions and deeper branding. If your store was auto-upgraded in August 2026, audit tracking first. If you need a custom extension or Function built, our Shopify app development team can help.

Frequently asked questions