On August 26, 2026, Shopify's checkout extensibility migration deadline hits and every store on every plan loses access to Additional Scripts, Thank You page script boxes, and Order Status page scripts. If you've pasted Google Ads conversion tracking, Meta pixel code, affiliate scripts, or any custom JavaScript into those boxes — and most merchants have — it all stops firing that day. No warning popup. No gradual sunset. Just silence where your data used to be.

The merchants who haven't migrated won't notice immediately. Their store will keep taking orders. But their Google Ads campaigns will stop reporting conversions. Their ROAS numbers will drop to zero overnight. They'll panic, think their ads broke, pause spending, and lose a week of revenue before someone figures out the problem was never the ads — it was the checkout migration they kept postponing.

What Does the Shopify Checkout Extensibility Migration Actually Remove?

Shopify is replacing its legacy script injection system with a structured, sandboxed framework called Checkout Extensibility. The old system let you paste raw JavaScript anywhere. The new system gives you specific tools for specific jobs.

Here's what's going away and what takes its place:

Additional Scripts (Settings > Checkout) — replaced by Web Pixels in Settings > Customer Events
Thank You page scripts — replaced by Web Pixels that fire on the checkout_completed event, plus Thank You page extensions for custom content
Order Status page scripts — replaced by Order Status extensions
checkout.liquid customizations (Plus only) — replaced by Checkout UI Extensions, which are React-based components built through the Shopify CLI
Shopify Scripts for payment/discount logic — replaced by Shopify Functions, which run server-side

The replacements aren't worse. In many cases they're more reliable — Web Pixels fire in a sandboxed environment that ad blockers can't touch. But the migration isn't automatic. Nobody moves your scripts for you.

The Conversion Tracking Migration Is the Most Urgent Step

Most merchants will feel the pain here first. If you're running Google Ads or Meta ads and your conversion tracking lives in Additional Scripts or the Thank You page box, you need to move it to Customer Events before August 26.

For most merchants, the fix takes 15 minutes:

Go to Settings > Customer Events in your Shopify admin
Check if the Google & YouTube channel is installed. If not, install it — this creates a managed pixel that handles conversion tracking automatically
Do the same for the Facebook & Instagram channel if you're running Meta ads
Open Settings > Checkout and look at what's in your Additional Scripts box. Copy it somewhere safe before it disappears
For any custom tracking scripts (affiliate platforms, analytics tools, Klaviyo), check with each vendor — most have already released Customer Events integrations

The catch: Web Pixels run in a sandboxed iframe. They can't access document.cookie, localStorage, or the main page DOM. If your attribution model depends on reading first-party cookies set elsewhere on the site, that specific method breaks. The managed pixels from Google and Meta handle this correctly. Custom implementations need to use the analytics.subscribe() API instead of raw DOM access. If you're already dealing with pixel issues, our guide on server-side tracking setup for Shopify covers how to get accurate conversion data regardless of browser limitations.

Don't skip the testing step. Install Google Tag Assistant and place a real test order after migration. Verify the purchase event fires with the correct transaction value. One merchant in the Shopify Community forums migrated their Google tag but forgot to map the revenue field — they ran campaigns for three weeks with conversions reporting at $0 value, which destroyed their Smart Bidding performance.

COD Merchants Have an Extra Layer of Migration Work

If you sell cash on delivery, your checkout probably has customizations that go beyond tracking pixels. Many COD merchants added custom phone fields, delivery note inputs, or alternative address fields through checkout.liquid or third-party apps that inject into the checkout. All of that needs to move to Checkout UI Extensions.

The specific things that break for COD stores:

Custom phone verification at checkout — OTP flows injected via JavaScript stop working. The replacement is a Checkout UI Extension that calls your verification API from a designated extension target.
Conditional payment method visibility — If you used scripts to hide COD above certain order values, or show it only for specific regions, you need to rebuild that logic as a Shopify Function using the Payment Customization API.
COD surcharges — Extra fees added at checkout via scripts need to move to the Cart Transform API.
Minimum order enforcement for COD — Same story. Shopify Functions can hide COD as a payment option below your threshold.

This is more complex than the tracking migration. Building a custom Checkout UI Extension requires the Shopify CLI and some React knowledge. If you're not technical, you'll need to find an app that provides these extensions or hire a developer. For background on how Shopify's checkout customization system works, see our checkout customization guide.

One shortcut worth knowing: if you capture customer details through a pre-checkout order form — tools like EasySell collect phone numbers, delivery notes, and custom fields before the customer ever reaches Shopify's checkout — those fields aren't affected by the migration at all. The data collection happens upstream. You still need to migrate your tracking pixels, but the form customization piece is already handled.

The 5 Mistakes That Catch Merchants During Migration

1. Not auditing what's actually in your script boxes. Go to Settings > Checkout right now and read what's pasted there. Most merchants added scripts months or years ago and forgot. You might find tracking pixels from ad platforms you no longer use, loyalty program integrations, affiliate tracking code, or custom analytics. Document everything before it vanishes.

2. Assuming the managed pixels handle everything. The Google & YouTube channel covers standard conversion tracking. But if you've added custom Enhanced Conversions parameters, custom audience signals, or non-standard event tracking, you'll need a Custom Pixel in addition to the managed one.

3. Forgetting about apps that inject into checkout. Some of your installed apps rely on checkout.liquid or Additional Scripts to function. Check with every app that touches your checkout flow — reviews, trust badges, loyalty programs, shipping estimators. Ask each vendor: "Are you compatible with Checkout Extensibility?" If they haven't migrated, you need to find an alternative before August 26.

4. Not testing on mobile after migration. Checkout UI Extensions render differently on mobile than desktop. An extension that looks fine on your laptop might break the checkout flow on a phone screen. Place test orders on an actual phone — not just a browser's mobile preview.

5. Migrating everything the last week of August. Checkout Extensibility has been available since 2023. The deadline has been extended multiple times, which trained merchants to procrastinate. This time, Shopify has committed to the cutoff. If your conversion tracking breaks on August 26 and you haven't tested the replacement, you'll lose days of data you can't recover.

The 4-Week Migration Timeline

You don't need to do this all at once. Spread it across four weeks and you'll catch problems before they become emergencies.

Week 1: Audit. Copy everything from your Additional Scripts, Thank You page, and Order Status page script boxes into a document. List every app that touches checkout. Screenshot your current checkout flow on desktop and mobile.

Week 2: Tracking migration. Install managed pixels (Google & YouTube, Facebook & Instagram channels). Create Custom Pixels for any remaining tracking scripts. Verify all events fire using debug tools and test orders.

Week 3: Checkout logic migration. If you have conditional payment method rules, custom fields, or surcharge logic, rebuild these using Shopify Functions and Checkout UI Extensions. COD-specific logic goes here. Install apps that provide the extensions you need.

Week 4: Testing. Place test orders through every checkout path — desktop, mobile, COD, prepaid, different product combinations. Compare conversion data in Google Ads and Meta against actual orders. Verify custom field data appears correctly in the order admin.

How Do You Check Your Shopify Checkout Migration Status?

Go to Settings > Checkout in your Shopify admin and look for a yellow warning banner. If you see one, your store has deprecated scripts that need to move before August 26, 2026.

Even if you don't see a banner, check your Additional Scripts box. If there's any JavaScript in there, it needs to move to Customer Events before August 26. If the box is empty, you're likely already on the new system — but verify by checking Settings > Customer Events to make sure your tracking pixels are active there.

The merchants who migrate in April have four months of clean data before the deadline. The merchants who migrate in August have zero margin for error. The tracking setup is the same either way — the only difference is whether you catch problems while there's still time to fix them.