Most DTC brands are treating the Shopify Checkout Extensibility migration as a compliance task. Something to hand to a developer, tick off, and move on. That is a mistake. The brands who understand what is actually happening will come out of August with better tracking, cleaner attribution, and a meaningfully higher AOV. The ones who do nothing will come out with broken ad accounts and no idea why their conversions fell off a cliff.
This is what you actually need to know, broken down for operators. No developer jargon, no fluff.
What Is Actually Happening on August 26
Shopify is retiring its legacy checkout customisation system. The old system let you paste raw JavaScript into a field called Additional Scripts in your Checkout settings, and into script boxes on the Thank You and Order Status pages. Virtually every Shopify store has been using this for years to fire conversion pixels, pass order data to Google Ads, track affiliate conversions, and customise what customers see after they buy.
On August 26, 2026, that field becomes read-only for all stores on every plan. Whatever is in there right now will stop executing. Not slow down, not partially break. Stop entirely.
If you have Google Ads conversion tracking in Additional Scripts, it stops on August 26. Your reported ROAS drops to zero overnight. Your campaigns lose signal, broaden targeting, and your CPAs spike. This has already happened to Shopify Plus stores who missed the earlier deadline.
The full list of what stops working:
- →
Google Ads conversion tracking (any tag pasted into Additional Scripts or the Order Status page)
- →
Meta Pixel purchase events fired from the Thank You page
- →
Affiliate and partner tracking scripts
- →
Custom analytics and attribution tools injected via script boxes
- →
Checkout.liquid visual customisations, brand elements, progress bars, custom upsell blocks built in the old system
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Cash on delivery and custom payment logic built with legacy scripts
The timeline is hard. There is no opt-out. Shopify began auto-migrating Plus stores in mid-2025 and is now rolling through standard plans ahead of the August cutoff.
What Checkout Extensibility Actually Is
Checkout Extensibility is Shopify's structured replacement for everything the old system allowed. Instead of open script injection, you now use specific tools for specific jobs.
Web Pixels (replaces Additional Scripts)
Customer Events in your Shopify admin replaces the Additional Scripts field. You install Web Pixels here, and they fire on specific events like checkout_completed, page_viewed, and cart_updated. Google Tag Manager, Meta, TikTok, and all major ad platforms now have native Web Pixel integrations. These actually pass first-party data better than the old script approach, which means your CAPI attribution improves after migration.
Checkout UI Extensions (replaces checkout.liquid)
This is where the AOV opportunity lives. Checkout UI Extensions let you add blocks directly into the checkout, thank you, and order status pages. You can render product recommendations, custom fields, gift messages, trust signals, upsell offers, and more, all without touching a single line of legacy code. These blocks render natively within the Shopify checkout UI, so they are fast, mobile-optimised, and conversion-safe.
Shopify Functions (replaces Script Editor)
Functions handle custom business logic: tiered discounts, custom shipping calculations, payment method customisation, and checkout validation rules. If you had custom discount logic built in the old Script Editor, Functions is what replaces it.
The AOV Opportunity Most Brands Are Missing
Here is the thing. Checkout Extensibility is not just a compliance migration. It is the most underused AOV lever in DTC right now, and the brands who treat it as an opportunity rather than a chore will come out of August with meaningfully higher revenue per order.
The old checkout.liquid system was locked for most stores, and any upsell attempts felt bolted-on. Checkout Extensibility changes this. You can now add native, single-click upsell blocks directly above the pay button. No redirect, no new tab, no friction. The customer sees a relevant offer in context, clicks once to add it, and checks out.
What the data shows
Pre-purchase upsell blocks above the pay button convert at 8-15%, significantly above standard on-site upsell benchmarks of 2-4%
Brands stacking a pre-purchase upsell with a post-purchase offer see 15-25% AOV lifts without any increase in ad spend
A fragrance brand saw a 46% AOV uplift during BFCM 2024 using tiered gift-with-purchase rules built on Checkout Extensibility
A case study across three Shopify Plus stores showed a combined $36,000 in additional revenue from mystery upsell offers at checkout
Adding a single well-targeted checkout upsell at 1% conversion rate on $1M GMV generates $10k in incremental revenue per year, with zero additional acquisition cost
The checkout is the highest-intent moment in your entire customer journey. The customer has already decided to buy. They have entered their card details. The question they are asking right now is not whether to buy, it is how much to buy. A well-placed offer at this moment converts at multiples of any other part of your funnel. And yet most DTC brands leave this page completely blank.
What to offer and how to structure it
Pre-purchase upsell block
8-15% conversion rateA single product offer placed directly above the pay button. Best practice is one offer, directly relevant to what is in the cart, framed as a bundle or completion item. Adding a warranty, a refill, or a complementary product at a discount converts far better than a generic cross-sell. The copy matters: 'Add X for Y' converts better than 'You might also like'.
Gift-with-purchase threshold
Lifts AOV 15-25%A dynamic bar that shows how far the customer is from a free gift. This drives AOV by pulling orders up to the threshold. The psychological mechanism is loss aversion. Customers do not want to miss the gift they are already close to earning. Set the threshold 10-15% above your current average order value for maximum lift.
Post-purchase one-click offer
5-12% conversion rateAn offer shown on the Thank You page, before the customer leaves, that can be added to their order with a single click and no re-entering of payment details. This is where subscription offers, subscription upsells, and subscription conversion rates are strongest. A customer who just bought your supplement is highly receptive to a subscribe-and-save offer at this exact moment.
The Migration Checklist: What to Do Before August 26
Run this in order. Do not skip the audit step. Brands who jump straight to implementation often break tracking they did not even know they had.
Audit everything in Additional Scripts and Order Status
Go to Settings, then Checkout in your Shopify admin. Open the Additional Scripts field and copy everything out. Do the same for the Thank You and Order Status page script boxes. List every pixel, tag, and script. Note which platform or tool it belongs to. This is your migration manifest. You cannot fix what you have not mapped.
Rebuild tracking via Web Pixels in Customer Events
Navigate to Settings, then Customer Events. Search for your existing platforms. Google, Meta, TikTok, Pinterest, and most major analytics tools now have native Web Pixel integrations here. Install them. They will pass first-party data more reliably than the old script approach because they fire within Shopify's sandboxed environment, which improves CAPI matching rates. Any platform without a native pixel will need a developer using Shopify's Web Pixels API.
Migrate checkout.liquid customisations to UI Extensions
If you have custom checkout design elements, trust badges, brand messaging, or upsell blocks built in checkout.liquid, these need to be rebuilt as Checkout UI Extensions. For most brands, this means choosing an app that provides the blocks you need, installing it, and configuring offers through the app dashboard rather than writing code. No developer required for standard upsell and trust elements.
Migrate Script Editor discounts and logic to Shopify Functions
If you have custom discount logic, tiered pricing rules, or conditional shipping built via the Script Editor, these need to be rebuilt with Shopify Functions. This is the most technically demanding part of the migration and the one most likely to need a Shopify developer. Start here early if you have complex checkout logic.
Install and configure your AOV extensions
Once tracking is stable, install your checkout upsell app of choice. Configure one pre-purchase offer to start. Run it for two to three weeks to get clean baseline data. Then layer in a post-purchase offer. Then a gift-with-purchase threshold if your product margins support it. Add layers incrementally so you can measure the impact of each one separately. Do not stack everything at once.
Test thoroughly before going live
Place test orders through the full checkout flow and verify that all conversion pixels fire correctly in your ad platform event managers. Check that upsell blocks render correctly on mobile, which is where 65-75% of DTC checkouts happen. Verify that post-purchase offers complete without re-entering payment details. Do not push live without at least 10 test orders across different cart configurations.
Which Apps to Use
A critical point on app selection: any upsell app you install must use native Checkout UI Extensions. Several legacy apps still operate by injecting scripts into the checkout page. Those will break in August for the same reason your existing pixels will break. Ask explicitly before installing any app.
Aftersell
Pre-purchase checkout blocks and one-click post-purchase upsellsPurpose-built for Checkout Extensibility. Native blocks, strong analytics dashboard, rules-based offer targeting.
Reconvert
Post-purchase upsell sequences and Thank You page personalisationDeep customisation of the post-purchase journey, including multi-step upsell sequences and dynamic recommendations based on what was purchased.
Checkout Components by Anvil
Checkout upsells with no commission modelFlat monthly fee instead of revenue share, which makes it more cost-effective at higher GMV. Native Checkout Extensibility blocks.
Bundler / Bundle Builder
Bundle offers at checkout to lift AOV through product combinationsWorks well for brands where bundling complementary products at a discount is the natural upsell, common in supplements, food, and skincare.
The Brands That Get This Right Will Pull Away
I worked with a CPG wellness brand doing around 85k per month in Shopify revenue. Their checkout was completely vanilla. No upsells, no trust signals, no post-purchase offers. They had tracking scripts in Additional Scripts that they had not touched in two years.
We used the migration as a forcing function. Rebuilt their tracking properly in Customer Events, which immediately improved their Meta CAPI match rate from 62% to 81%. Added a pre-purchase upsell for a complementary product. Set a gift-with-purchase threshold at 20% above their existing AOV. Added a subscribe-and-save offer on the Thank You page.
Within 60 days, their AOV was up 22%. Their subscription conversion rate from first-time buyers was up 8 percentage points. Their Meta ROAS improved not because they changed their ads but because attribution got cleaner and the algorithm got better signal. And they were fully compliant ahead of the deadline.
Most brands will treat August 26 as a deadline to survive. The operators who treat it as a revenue opportunity will come out the other side with better tracking, cleaner attribution, and a checkout that actually works for them. That is the difference between operating reactively and operating with intent.
Growth Audit
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I will audit your current checkout setup, map every script that will break in August, and build you a migration plan that fixes tracking and adds AOV extensions in the same sprint. No agency overhead, no fluff.
Book Your AuditFrequently asked questions
What is Shopify Checkout Extensibility?
Shopify Checkout Extensibility is the replacement for legacy checkout customisation tools including checkout.liquid and Additional Scripts. It provides a structured, sandboxed framework using Checkout UI Extensions for visual blocks, Web Pixels for tracking, and Shopify Functions for custom business logic. It gives you specific tools for specific jobs rather than open script injection.
What breaks on August 26, 2026 if I do not migrate?
Additional Scripts, Thank You page script boxes, and Order Status page scripts stop executing on August 26, 2026 for all Shopify stores. This means Google Ads conversion tracking, Meta pixel purchase events, affiliate tracking scripts, and any custom JavaScript pasted into those fields will stop firing. Your ad platform ROAS reports will drop, campaigns will lose signal, and CPAs will spike.
How much AOV uplift can Checkout Extensibility deliver?
Pre-purchase upsell blocks convert at 8-15%, well above standard on-site upsell benchmarks. Stacking a pre-purchase upsell with a gift-with-purchase threshold and a post-purchase offer typically delivers 15-25% AOV increases without additional acquisition spend. One fragrance brand saw a 46% AOV boost during BFCM using tiered gift-with-purchase rules built on Checkout Extensibility.
Do I need Shopify Plus to use Checkout Extensibility?
No. Checkout Extensibility is available on all Shopify plans. Standard stores get access to Checkout UI Extensions, Web Pixels, and most Shopify Functions. Shopify Plus unlocks additional customisation depth but most meaningful AOV improvements, including pre-purchase upsells and post-purchase offers, are available on every plan.
What are the best apps for checkout upsells in 2026?
Aftersell, Reconvert, and Checkout Components by Anvil are the leading options purpose-built for Checkout Extensibility. When evaluating any app, confirm it uses native Checkout UI Extensions and not legacy script injection. Apps using script injection will break in August for the same reason your current pixels will break.
How long does the Checkout Extensibility migration take?
A clean migration for a standard Shopify store typically takes two to four weeks. Most of the time is spent auditing existing scripts, rebuilding tracking via Web Pixels, and testing in a development environment. Stores with heavy checkout.liquid customisations or complex COD and discount logic should allow four to eight weeks and involve a Shopify developer.
About the author
Caner Veli built Liquiproof from zero to 3,000+ global retailers in under 6 years. He now helps DTC and CPG brands fix broken growth engines and scale 2x-15x in 90 days.