If you’re running a Shopify Plus store and haven’t migrated to Checkout Extensibility yet, you’re in a tight spot. The August deadline passed months ago, and the January 2026 automatic upgrades are just around the corner.
For merchants who missed the deadline, this isn’t just a warning anymore. Your checkout customisations are currently in a locked state, your conversion tracking may already be broken, and you have a narrow window to fix everything before Shopify automatically upgrades your store and removes all legacy code.
But here’s the thing: you still have time to fix this properly. Here’s what’s happening and what you need to do.
What’s Already Happened Since August 2025
Since the August 28, 2025 deadline passed, Shopify has been systematically disabling legacy checkout features. Here’s what’s already changed:
Additional scripts on Thank You and Order Status pages are now view-only and cannot be edited. If you try to modify them, Shopify blocks the changes. Any new stores or stores that upgrade voluntarily can no longer use additional scripts at all.
Personal information like customer email addresses and phone numbers is no longer accessible through additional scripts. This means any custom tracking or analytics that relied on passing customer data has already stopped working properly.
Apps using script tags have been shut down completely. If you were relying on older apps that hadn’t updated to Checkout Extensibility, those features disappeared after August 28. Checkout.liquid customisations on Thank You and Order Status pages have stopped rendering. Any custom HTML, CSS, or JavaScript you had in those templates is no longer visible to customers.
What’s Coming in January 2026
The situation becomes even more critical in just a few weeks. Starting January 2026, Shopify will begin automatically upgrading all remaining stores that haven’t migrated. This isn’t optional, and there’s no way to postpone it.
When your store is automatically upgraded, Shopify will completely remove all legacy customisations. Your additional scripts will be deleted. Your checkout.liquid code will be removed. Any script tags from apps will be permanently disabled.
The upgrade happens automatically without warning. You won’t get advance notice of the exact date your store will be upgraded. One day your legacy customisations will simply be gone.
Unlike the previous deadlines where stores had some flexibility, the January 2026 automatic upgrades are final. Once Shopify removes your legacy code, there’s no rollback option and no way to recover it.
What Will Break (And What You Need to Fix)
Most Shopify Plus stores have at least some customisations that will be affected. Here are the most common issues we see when helping merchants migrate:
Conversion Tracking and Analytics
This impacts nearly every store. If you’ve added Google Analytics, Facebook Pixel, TikTok Pixel, or any other tracking code to your checkout through the “Additional Scripts” section, all of that stops working after the deadline.
The fix requires either installing official Shopify apps (like the Google & YouTube app or Facebook & Instagram app) or building custom tracking pixels using Shopify’s Customer Events API. For most standard tracking needs, the official apps handle everything automatically. For custom tracking requirements or less common platforms, you’ll need development work.
Custom Checkout Fields
Many stores added custom fields to collect gift messages, delivery instructions, or business buyer information. If these were added through checkout.liquid code, they need to be completely rebuilt as Checkout UI Extensions.
The good news is that the new system is actually more powerful. You can create validated fields, conditional logic, and even integrate with Shopify Functions for dynamic behavior based on customer inputs.
Post-Purchase Features
Custom upsells, surveys, or interactive content on your Thank You page that was added through JavaScript will all stop working. These need to migrate to dedicated post-purchase extensions or Thank You page UI extensions.
Third-Party Apps
Even if you didn’t customise checkout yourself, apps you’ve installed may have used script tags to add functionality. Not all app developers have updated to Checkout Extensibility yet, so some apps simply won’t work after the deadline.
Your Shopify admin has an upgrade guide that lists which of your installed apps are incompatible. You’ll need to either get updated versions from the developers or find replacement apps.
What Good Looks Like After Migration
Don’t mean to sugarcoat the effort required, but there are real benefits once you’re on the other side of this.
Your checkout will actually load faster. The old system had all this JavaScript blocking page renders, slowing everything down. With the new sandboxed approach introduced through Checkout Extensibility, code runs asynchronously, and most stores see noticeably faster checkout experiences. Faster checkout means better conversion rates—that’s been proven over and over.
Shop Pay becomes a real option. You know how Shop Pay users convert 50% better than regular checkout? You couldn’t really use it before if you had customisations. Now you can have your custom fields AND Shop Pay working together seamlessly.
Your tracking gets more reliable too. Once it’s set up correctly with the new system, it’s actually more stable than the old method. Browser updates and privacy changes don’t break it as easily.
And honestly, the peace of mind is worth something. You’re not constantly worried about the next Shopify update breaking your checkout. The new system is future-proof in a way the old one never was.
Your Game Plan for the Next Few Weeks
Alright, here’s what you need to do, broken down into manageable steps.
Get clarity on what you’re dealing with. Go to Settings > Checkout in your Shopify admin and look at the upgrade guide. It’ll show you exactly what customisations you have and which apps are incompatible. Write it all down.
Focus on getting your tracking fixed first. For anything custom or less common platforms, you’ll need developers to build proper pixels.Check all your apps during this time too. Some might have updated versions that work with the new system. Others might need to be replaced entirely.
Within a month: Get your custom functionality rebuilt. This is where you recreate any custom checkout fields, post-purchase features, or unique business logic. This part requires development expertise—don’t try to wing it.
Test everything thoroughly before you go live. Run test orders with different scenarios. Check your analytics to make sure events are firing. Verify on mobile and desktop.
Launch carefully: Pick a low-traffic time to deploy everything. Watch your conversion rate, check that tracking is working, make sure there are no errors popping up.
Getting This Done Before Deadline
Nobody wants to deal with forced platform migrations during their busiest season. But the reality is that waiting isn’t making this any easier. It’s just making it more expensive and riskier.
If you need help, hire someone who actually specialises in this. Make sure they understand the January timeline and can prioritise your work.
Be prepared for premium pricing if you need it done fast. Good developers are slammed right now with emergency migrations. But it’s still worth it compared to the alternative of broken checkout and lost revenue.
Your checkout is the final step of your customer journey and often the difference between a sale and an abandonment. Don’t let a missed deadline derail it. Checkout Extensibility is now the standard, and getting it right is non-negotiable.
As a certified Shopify Plus Partner, reach out to Sweans if you need support completing your migration on time. We can help you transition smoothly and ensure your checkout is fully ready for Shopify Checkout Extensibility.
