Migrating From checkout.liquid to Checkout Extensions on Shopify Plus

Key takeaways

• checkout.liquid is fully switched off. The Information, Shipping and Payment steps dropped it on August 13, 2024, the Thank you and Order status pages followed on August 28, 2025, and Shopify auto-upgraded the holdouts from January 2026.
• Four tools replaced the one file: checkout UI extensions for interface, Shopify Functions for logic, the branding API for styling, and web pixels for tracking.
• The migration is an inventory-and-mapping exercise. List what your checkout.liquid did, assign each item to its new tool, rebuild in a draft checkout configuration, and publish.
• A good share of it needs no developer. Branding, layout, app blocks and custom pixels are admin work. Custom UI extensions, Functions and app pixels are developer work.
• A few things have no 1:1 replacement, including arbitrary DOM edits and per-page styling. Plan workarounds instead of waiting for parity.

A checkout.liquid to extensions migration in 2026 is no longer a forward-planning exercise. Every deadline has passed, the file is off, and any Shopify Plus store that did not move was upgraded automatically.

That changes what this guide is for. If your discount logic died with Shopify Scripts on June 30, if your thank-you page tracking disappeared in the January auto-upgrades, or if you have been running a near-default checkout since the switch and want your customizations back before BFCM, this is the rebuild playbook.

Our older guide to modifying checkout.liquid in Shopify Plus documents the legacy system this piece replaces. For the full map of the replacement framework, see our complete guide to Shopify checkout extensibility - this article stays on the practical path from old to new.

Why you can trust us

We have been in the Shopify space for over four years and have worked with hundreds of Shopify brands on their storefronts, including stores that went through this exact upgrade. We build Fudge, an AI storefront editor with a 4.9 rating on the Shopify App Store, so we work daily in the theme and admin layer this migration runs through.

Where the checkout.liquid shutdown stands in 2026

Every date in this table is past. It is here so you can work out which parts of your old setup broke when, and what you are actually rebuilding.

Two details in that table matter for the work ahead.

Your old code is still readable. Additional scripts became view-only rather than deleted², and the checkout.liquid file may still sit in your theme’s code editor. That makes the audit in step 1 possible without archaeology.

The auto-upgrade did not migrate anything. Stores upgraded in January 2026 lost their legacy customizations outright². If your checkout looks bare today, that is why.

What replaced checkout.liquid?

One editable file became four sandboxed tools, each owning a slice of what checkout.liquid used to cover.

• Checkout UI extensions render custom interface at defined targets in checkout and on the Thank you and Order status pages.⁵
• Shopify Functions run backend logic: discounts, delivery and payment customization, and cart and checkout validation.⁶
• The branding API styles checkout through design tokens set with the checkoutBrandingUpsert mutation in the GraphQL Admin API.⁷⁸
• Web pixels subscribe to customer events in a sandbox and replace the additional scripts field for tracking.⁹

The checkout extensibility pillar guide covers each tool in depth. What you need here is the mapping.

Step 1: Audit what your checkout.liquid actually did

Before rebuilding anything, produce a flat list of every job the old checkout performed. Most Plus checkouts accumulated years of snippets nobody documented.

Pull the evidence from three places:

1. The old checkout.liquid file, still visible in the theme code editor on themes that had one. Read it top to bottom and note every non-standard block.
2. The view-only additional scripts field, which preserves the exact tags that used to fire on the Thank you and Order status pages.²
3. Your app list. Any app that injected script tags into checkout stopped working at the sunset dates, so check each checkout-touching app for an extensibility-ready version.

Sort every finding into one of six buckets: tracking, trust content, custom fields, upsells, validation, styling. Each bucket maps to exactly one row of the table above.

Then prune. A migration is the cheapest moment you will ever get to drop the pixel from a defunct ad platform or the badge for an expired certification. Rebuild only what still earns its place in the highest-converting page you own.

Step 2: Rebuild the merchant-side pieces in a draft checkout

Shopify’s admin calls the unit of checkout customization a checkout configuration. The Admin API still calls it a checkout profile, which is why the branding mutation takes a checkoutProfileId.⁸ Either way, it is a versioned bundle of branding, layout and blocks that you can stage as a draft and publish when ready.¹⁰

The flow in the admin:

1. Go to Settings > Checkout. In the Configurations section, click Duplicate next to your active configuration to create a draft.¹⁰
2. Click Edit on the draft to open the checkout and accounts editor.¹⁰
3. Set your branding: logo, background, colors and fonts across the checkout, Thank you and Order status pages.¹¹
4. Pick your layout. The editor’s settings let you switch between one-page and three-page checkout; one-page is the default.¹²
5. Add app blocks for trust badges, upsells and custom content, positioning them in the editor.
6. Preview the draft, then click Publish. Publishing swaps it in as the active configuration, and the old active one becomes a draft you can roll back to.¹⁰

None of this requires code, and the draft-first flow means the live checkout never sees a half-finished state. Our guide on adding trust badges to Shopify checkout walks the block-based version of the most common single customization.

Step 3: Move tracking to web pixels

Tracking is the piece most Plus stores lost without noticing, because the failure is silent: the checkout works, the ad platforms just stop receiving conversions.

You have two replacements for the old additional scripts tags.⁹

App pixels run in a strict sandbox and come from the app for that platform - Google, Meta, TikTok and the rest maintain their own. This is the default choice: the vendor keeps it current and it needs no code from you.

Custom pixels are pasted in the admin’s pixel manager and run in a more permissive sandbox with the events API pre-wired.⁹ They are the escape hatch for platforms without an app pixel. Two caveats: Shopify states plainly that custom pixels are unsupported and that compliance, security and upkeep are your responsibility, and not all pixel functionality works inside the sandbox.¹³

Either way, verify with a real test order that checkout_completed reaches every platform you care about. For ad platforms specifically, pair the pixel with a server-side path; our guide to Meta CAPI on Shopify covers deduplication and event match quality for exactly this setup.

Step 4: Rebuild custom UI and logic with a developer

Two buckets from your audit are genuine development work.

Custom checkout UI extensions

Anything an app block cannot cover - a bespoke custom field, a conditional banner, a survey on the Thank you page - becomes a checkout UI extension. Extensions render at defined static or block targets, are built from Shopify’s checkout components, and run in an isolated sandbox with no access to the checkout page’s HTML or to payment data.⁵

Extensions on the Information, Shipping and Payment steps are a Plus capability; the Thank you and Order status page targets are open to all plans.⁵ A developer scaffolds them with the Shopify CLI, tests against a development store, and the merchant places block-target extensions in the same checkout editor from step 2.

Shopify Functions

Discount stacking rules, shipping rate rewrites and payment method gating that lived in Shopify Scripts now live in Shopify Functions, which compile to WebAssembly and run on Shopify’s infrastructure during checkout.⁶ Function APIs cover discounts, delivery and payment customization, cart and checkout validation, order routing and more.⁶

Since Scripts stopped executing on June 30, 2026, any store that skipped this port has been running without that logic for two months.⁴ If margins or shipping tables look wrong since early summer, start here.

Shopify publishes templates for Rust and JavaScript and recommends Rust for performance on large carts.⁶ Before commissioning custom Functions, check whether a discount or shipping app already ships the logic as configuration - for common rules, it usually does.

What has no 1:1 replacement

An honest migration plan names the gaps. Four things from the checkout.liquid era do not come back.

Arbitrary edits to checkout markup. Extensions cannot touch the page’s HTML at all - they render inside their own sandbox at the targets Shopify defines.⁵ If no target exists where your old snippet rendered, there is no way to render there. The workaround is the nearest target, or moving the element to the cart page, where your theme still rules.

Per-page styling. Branding applies across checkout, checkout UI extensions and customer account pages together; Shopify explicitly does not support styling individual pages.⁸ Design once for the whole flow.

Scripts that needed the checkout DOM. Session recording, some A/B testing tools and older affiliate tags read the page directly, and the pixel sandbox does not expose it.¹³ Ask each vendor for their app pixel or server-side integration; where neither exists, that tool is done in checkout.

Free network calls in logic. Functions cannot call external services directly. A fetch-target mechanism exists where Shopify performs a declared HTTP request on the function’s behalf, but it must be enabled by Shopify and is scoped to enterprise arrangements and specific use cases.¹⁴ The standard workaround is precomputing data into metafields the Function can read.

If one of these gaps is core to your checkout, decide the workaround now rather than mid-rebuild.

What the upgrade gives you

The trade for those limits is real, and it is the reason not to grieve the old file.

A faster, better-converting checkout. Shopify reports its checkout converts 15% better on average than the competition, and up to 36%, citing a 2023 study run with a major consulting firm.¹⁵ Those figures are Shopify’s own, but the direction matches what we see: less custom weight in checkout means less to slow it down.

Shop Pay on current rails. Shopify reports Shop Pay checkout is up to three times faster and converts as much as 50% better than standard checkout.¹⁵

One-page checkout as the default layout, with a one-click switch back to three pages if your data says otherwise.¹²

Updates handled by Shopify. This is the quiet one. Stores on checkout.liquid sat on a maintenance version that never received new checkout features automatically.³ On extensibility, your customizations talk to versioned APIs, so Shopify ships checkout improvements under you without breaking them.

Timing the rebuild before BFCM

Work backwards from late November.

• September: finish the audit and the merchant-side rebuild in a draft configuration. Commission any custom extensions and Functions now - developer queues fill up from October.
• Early October: publish, then place test orders and verify every pixel, Function and field on a live order.
• November: freeze. The checkout is the last place to ship changes during peak; keep a rollback draft of the working configuration.¹⁰

A checkout published in October has weeks of real orders to prove itself before Black Friday. One published in mid-November does not.

Where Fudge fits

Checkout extensions, Functions and pixels are their own toolchain, and Fudge does not build them.

What Fudge does own is everything the shopper sees before checkout: the landing pages, product pages, cart content and trust sections that decide whether checkout gets a visitor at all. Describe the change in plain language, and Fudge generates native Liquid, CSS and JavaScript in your theme as a draft you preview and publish - the same draft-first pattern the checkout editor uses.

While a developer rebuilds your checkout extensions, the page builder side of the BFCM prep does not need to wait on them.

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