Your Shopify Checkout Customisations Have Already Been Turned Off

What Is Shopify Checkout Extensibility?

Checkout extensibility is the replacement for editing checkout through theme code. Shopify's developer changelog describes it as checkout UI extensions and Shopify Functions to surface new functionality, the Checkout Branding API to customise styling, and Pixels to track events.

The migration is not optional and it is not upcoming. If you are on Plus and did nothing, Shopify acted on your behalf. Its Plus upgrade guide states that during the January 2026 automatic upgrades, "all page customizations on your legacy pages will be lost" and "all analytics scripts will be lost".

So the work in front of you is not a migration project. It is a damage assessment.

The Dates, And Which Have Passed

Five dates, verified against Shopify's own pages rather than from a summary.

| Date | What happened | Who | | --- | --- | --- | | 13 August 2024 | Deadline to move Information, Shipping and Payment pages off checkout.liquid | Plus | | 28 August 2025 | checkout.liquid and additional scripts sunset on Thank You and Order Status. Script tags sunset on those pages | Plus | | January 2026 | Automatic upgrades began. Customisations and analytics scripts lost | Plus | | 30 June 2026 | Shopify Scripts deprecated and deactivated | All plans that had Scripts | | 26 August 2026 | Script tags sunset on Thank You and Order Status | Non Plus |

The Failure Nobody Investigates

This is the part worth reading twice.

On 28 August 2025, checkout.liquid and additional scripts were sunset for the Thank You and Order Status pages. Shopify's Plus upgrade guide is specific about what else went with them. After that date, "additional scripts and checkout.liquid aren't editable", and "Personal Identifiable Information (PII) isn't accessible through your additional scripts, checkout.liquid, or checkout_completed pixel events".

On the stores I have worked on, those scripts are where the conversion tags live, along with server side tracking bridges and the event that reports a purchase and its value to an ad platform. Those scripts were sunset, so whatever was running inside them stopped running.

In my experience nothing turns red when that happens. There is no alert, no failed deploy, no error in an inbox. The store keeps taking orders perfectly well. What changes is the number of conversions your ad platform believes it caused.

A dashboard showing fewer attributed conversions reads as weak performance. The usual responses are to blame the creative, blame an algorithm update, or cut the budget on the channel. In my experience that is exactly what happens, and the channel being cut is often still working fine. The measurement broke, not the marketing.

If your Shopify conversion figures stepped down at some point after August 2025 and never recovered, check the checkout before you rewrite the ads.

What Happened If You Were Auto Upgraded

Shopify did not leave legacy pages running indefinitely. From January 2026 it began upgrading them automatically.

The upgrade guide states plainly that when this happens, all page customisations on the legacy pages are lost, and all analytics scripts are lost. It adds one qualifier worth reading: a limited number of analytics scripts might be moved to custom pixels, described as a best effort attempt to maintain continuity in measurement. Best effort on a limited number is not a migration, and it is not something to plan around.

The same section carries a change in the other direction. After an automatic upgrade, Shopify states that personally identifiable information is included again in checkout_completed events in pixels. So the PII gap described above belongs to the window between August 2025 and the upgrade, not to the state a Plus store is in now.

There is a specific unpleasantness here. An automatic upgrade produces a working checkout. The store does not go down. Nobody gets paged. The customisations simply are not there any more, and whether anyone notices depends entirely on whether someone was looking at that page.

The 2024 deadline carried the same shape. Shopify's changelog warned that "Checkouts that aren't upgraded on time will be automatically upgraded to an un-customized, out-of-the-box Shopify Checkout". Working, and stripped.

Scripts Stopped On 30 June 2026

Separate change, same month, and in my experience frequently confused with the checkout page dates.

Shopify's help documentation states: "As of June 30, 2026, Shopify Scripts has been deprecated. Any Scripts that were still published on your store have been deactivated and no longer work."

In my experience Scripts usually carried things like tiered discounting, a shipping rule or a payment method restriction. Whatever yours did, if it was still published it stopped. The replacement is Shopify Functions, which Shopify describes as letting developers create custom commerce experiences in a similar way, executing in under 5 milliseconds and distributed as apps.

Functions are a genuinely better home for that logic, and I have written separately about What Belongs In A Shopify Function. The relevant point here is that the move was not optional and the deadline is behind you.

Example: Lost Thank You Page Scripts And A Misread Ad Channel

This is a constructed example, not a client engagement. It is built only from the documented behaviour set out above, to show how that behaviour presents to the people looking at the numbers.

Take a Plus merchant with a mid sized catalogue, running paid social as the main acquisition channel. Their Thank You page carries two additional scripts: a conversion pixel, and a small script pushing order values into a reporting sheet.

They are auto upgraded. Per Shopify's guidance, the page customisations and the analytics scripts are lost. Nothing breaks visibly and orders continue.

From that point the conversion pixel is no longer running, so the ad platform is not told about those purchases. Reported cost per acquisition rises. The obvious internal read is that the channel has degraded.

If spend is cut on that basis, revenue falls, which appears to confirm the diagnosis. Reported revenue and real revenue have come apart, and nothing in the process prompts anyone to compare the two.

The tell would be that platform reported conversions no longer match the Shopify order count, and that the gap starts on a specific date rather than drifting. A drift is a performance story. A step change on one date is a technical one.

The fix is to rebuild the tracking as web pixels under the new architecture.

The lesson I take from it is to reconcile platform conversions against Shopify orders whenever a channel appears to fall off. It is a short check, and it distinguishes a marketing problem from a plumbing one.

One Deadline Is Still Ahead

26 August 2026. Script tags are sunset on the Thank You and Order Status pages for non Plus stores. That is on shopify.dev, and at the time of writing it is weeks away rather than months.

If you are not on Plus and you have apps that inject anything into those pages through script tags, they stop. I would expect it to feel like the Plus experience from August 2025, with no outage and nothing obviously wrong on the page, but that is my expectation rather than anything Shopify has stated about this date.

The check is short. List what currently runs on the Thank You and Order Status pages, identify anything arriving through a script tag, and confirm whether the app behind it has shipped a pixel or extension based replacement. My own expectation is that apps which have not moved by now are unlikely to.

This is the one place in this article where acting early still helps. You can also Request The Free Shopify Store Audit.

What Replaces It

Shopify's route forward is Extensions in Checkout. The four pieces, per the developer changelog: checkout UI extensions and Shopify Functions for new functionality, the Checkout Branding API for styling, and Pixels for event tracking.

The upgrade guidance is that customisations are recreated using blocks and web pixels, or by moving to apps that support the new page architecture.

Two practical consequences worth planning around.

First, tracking moves to web pixels. That is a different model from dropping a script tag on a page, and in my experience it is the piece left until last, because it is invisible until it is missing.

Second, logic that used to sit in theme code needs a different home. In my experience a Function is usually the right one, though a checkout UI extension or an app can fit better depending on what the logic actually does. If you are weighing that up, see What To Settle Before You Build A Shopify App.

Signs Your Checkout Migration Is Unfinished

Five signals. Any one of them is worth an afternoon.

1. Your reported conversions from an ad platform stepped down on a specific date after August 2025 and did not recover.
2. Nobody can tell you what used to be on your Thank You page.
3. You are on Plus and cannot confirm whether you were auto upgraded in January 2026.
4. You had a Shopify Script and nobody has confirmed what replaced it since 30 June 2026.
5. You are not on Plus and an app still writes to your Order Status page through a script tag.

Signal one is the one I would check first, because it is the one costing money right now rather than the one that will.

Common Questions About Checkout Extensibility

Is checkout.liquid Still Supported?

No. Shopify's documentation states it is unsupported for the Information, Shipping and Payment steps, and that it was sunset alongside additional scripts for the Thank You and Order Status pages on 28 August 2025. Stores that did not migrate were subject to automatic upgrades beginning in January 2026.

What Happens If I Never Upgraded?

If you are on Plus, Shopify upgraded the pages for you. Its Plus guide states that during automatic upgrades all page customisations on legacy pages are lost, along with all analytics scripts. The warning attached to the 2024 deadline was similar, that unupgraded checkouts would become an un-customized, out-of-the-box Shopify Checkout.

Why Did My Ad Performance Drop After August 2025?

Two separate things happened on 28 August 2025. Additional scripts and checkout.liquid were sunset on those pages, so tracking running inside them stopped. Separately, personally identifiable information stopped being accessible through checkout_completed pixel events. Reported conversions can fall while real orders do not, which reads as underperformance.

Do Shopify Scripts Still Work?

No. Shopify states that as of 30 June 2026 Shopify Scripts has been deprecated, and any Scripts still published on a store have been deactivated and no longer work. The replacement is Shopify Functions, which Shopify describes as executing in under 5 milliseconds and distributed as apps.

Is There A Deadline Left For Non Plus Stores?

Yes, 26 August 2026, when script tags are sunset on the Thank You and Order Status pages for non Plus stores. It is the only date in this timeline still ahead. If an app writes to those pages through a script tag, confirm it has a pixel or extension based replacement.

Part of The Shopify Development Guide. See also Migration And Replatforming and Themes And Online Store 2.0, and the Shopify Services Listed On The Main Site.