Shopify checkout apps: what merchants can actually customize now

Shopify checkout customization in 2026 runs on Checkout Extensibility: branding and apps you place in the checkout and accounts editor, not checkout.liquid. Plus merchants can put app blocks on information, shipping, and payment, and use deeper branding APIs. Everyone else still gets the editor for logos and colors, app blocks on Thank you and Order status (Basic and higher, not Starter), web pixels, and Functions that ship inside public App Store apps.

Confirm dates in Settings → Checkout. Shopify’s Admin is the source of truth if a blog (including this one) disagrees with the banner in your shop.

Key takeaways

• checkout.liquid is gone for the three in-checkout steps (sunset 13 August 2024). Do not plan a project around it.
• Plus: in-checkout UI extensions, advanced branding, custom apps at checkout, custom Functions.
• Non-Plus: branding in the editor; Thank you / Order status app blocks; pixels; App Store Functions apps.
• Non-Plus stores using additional scripts / script-tag apps on Thank you and Order status face a 26 August 2026 upgrade line. After that, Shopify auto-upgrades and legacy scripts do not come along.
• The failure mode is silent: orders keep processing; Google Ads and Meta conversions can go dark.
• Shop Pay is part of the deal. Random DOM hacks are not.
• Post-purchase one-click upsell (after payment, before Thank you) is not the same as a Thank you page block.

What Checkout Extensibility replaced

For years, Plus merchants edited checkout.liquid like a theme file. That file could load anything. It also broke when Shopify shipped checkout, it fought Shop Pay, and it turned every app into a race to inject scripts. Checkout Extensibility replaces that with:

• Checkout and accounts editor — visual branding (logo, fonts, colors, some layout). Basic or higher.
• Checkout UI extensions — apps render in declared targets (blocks, line items, header, Thank you). Sandboxed. No free-roam DOM. Developer targets such as purchase.checkout.block.render versus purchase.thank-you.block.render live on shopify.dev.
• Web pixels — tracking in a sandbox, not a soup of tags in additional scripts.
• Shopify Functions — backend logic (discounts, some delivery/payment customization, validation). See build vs buy.

Shopify Scripts (the Ruby Plus feature) are also over: editing froze 15 April 2026 and Scripts stopped executing 30 June 2026. If a Plus store still “has a Script,” it does not. The replacement is Functions, usually delivered by an app.

If the setup instructions say “paste this into Additional scripts,” you are on a surface Shopify is deleting, not a strategy.

Plus vs regular plans: the honest matrix

Plan language below matches Shopify’s public split as of August 2026. “Grow” is the current name for the middle paid plan in Help Center copy for Messaging; your invoice may still say “Shopify.” The checkout split is Plus vs not-Plus, not the name on the bill.

Checkout Blocks, Shopify’s own block app, follows the same split: basic blocks more broadly, extra functionality on Plus. Always read the listing’s “works with” line for your plan. Do not take a screenshot of a Plus checkout as a Basic store promise.

The 26 August 2026 line (non-Plus Thank you / Order status)

Plus stores already passed their Thank you / Order status additional-scripts deadline (28 August 2025), with auto-upgrades afterward. Non-Plus stores that still rely on additional scripts or script-tag apps on those two pages have a hard close: Shopify has set 26 August 2026 as the date those pages move fully to extensibility.

This page was reviewed on 25 August 2026—the day before that line. If you are reading after the 26th, skip to the post-upgrade checks. If you are reading before it, do not wait for a storefront error. There usually is not one.

If you have not upgraded yet

1. Open Settings → Checkout. Copy every Additional Script into a document. After auto-upgrade the field is gone, not migrated.
2. List every app that appears on Thank you or Order status (survey, upsell, loyalty, tracking, “trusted badges”).
3. Check each listing for Checkout Extensibility / Thank you page app blocks.
4. Place replacements in the checkout and accounts editor. Do not paste scripts.
5. Place pixels in Settings → Customer events (official Google / Meta / TikTok pixels, or a custom pixel).
6. Complete a test order, including Shop Pay if you offer it.

If auto-upgrade already happened

1. Place a test order. Confirm Thank you still shows what you expect.
2. Check Google Ads, Meta, and any affiliate dashboard for purchase events over the next 24–48 hours—not only Shopify’s order list.
3. Re-add missing pixels in customer events. Re-add visible widgets as app blocks.
4. If an app has no extensibility version, replace the category using the same hygiene rules you use on the storefront.

Official channel apps may carry over. Custom tracking pixels, GTM pasted into Additional Scripts, and affiliate tags generally do not.

Upsells: three different products

Merchants say “post-purchase app” and mean three things:

1. In-checkout upsell — offer on information/shipping/payment. App blocks here are Plus.
2. Post-purchase extension — interstitial after payment, before Thank you, often one-click add to the order. Shopify has documented this as a specialized extension with tighter access. Do not assume every “upsell app” is this surface.
3. Thank you / order status block — after the order exists. Good for surveys, loyalty, “next order” codes, and some offers. Available on Basic and higher via apps. Conversion is not the same as a one-click post-purchase add.

Cart-page upsells (on the Online Store) are a fourth thing and have nothing to do with checkout extensibility except that too many of them plus checkout offers will annoy buyers. One offer moment per journey until you have data.

Unsupported hacks to refuse

Functions that hide payment methods or rewrite delivery options may be Plus-only even when the app is public—check the Function API availability table on Shopify Functions. Discount Functions in public apps are the common all-plan case. Custom Function apps require Plus, per Shopify’s Functions docs.

If an upsell app wants write_orders and a pile of customer scopes, read security and data access before you click Install.

Frequently asked questions

What to do next

Shopify checkout apps only help if they sit on a surface your plan allows. Place pixels in customer events, place widgets in the editor, and refuse paste-in scripts. Then keep the rest of the stack thin with the install protocol.