Developer / ToolsAction Required

With the Shopify AI Toolkit,
automatically migrate extensions to Polaris Web Components

A new skill that hands off API version updates and the move to Polaris Web Components for Checkout / Customer account UI extensions to an AI coding agent. It compresses manual work like React→Preact conversion and replacing legacy components.Migration is required on or after October 1, 2026.

On this page
  1. What's actually changing (understand it in 30 seconds)
  2. How it works: the flow of an AI agent handling the migration for you
  3. Three migration tasks the AI Toolkit handles for you
  4. Why the migration is "required": the 2026-10-01 deadline
  5. Why Polaris Web Components
  6. Getting started (3 steps)
  7. Five points engineers should keep in mind
  8. Three use cases you can apply at work
  9. A one-line summary for your pitch

1What's actually changing

The Shopify AI Toolkit now supports the work of upgradingCheckout UI extensionsandCustomer account UI extensionsto the new API version (i.e., Polaris Web Components).
By pairing it with your AI coding agent of choice, you can skip repetitive manual work and accelerate the heavy lifting of migration.

Before: manual migration

Developers had to work through the React→Preact rewrite, building and applying a mapping for legacy components, and updating the extension APIs one by one, all by hand.

Going forward: the AI handles it

The agent references the AI Toolkit plus the enhanced developer docs and runs the necessary migration steps in order. Developers can focus on review and finishing touches.

2How it works: the flow of an AI agent handling the migration for you

Developer Launch the AI agent AI Toolkit + enhanced developer docs (migration skill) Supplies the steps Runs the necessary migration steps ① React → Preact conversion ② Legacy → Polaris replacement ③ Extension API updates Polaris-migrated extensions API 2025-10 or later ⚡ Faster rendering Shippable on the latest version
The key point is that the AI Toolkit doesn't run on its own;it supplies migration skills and documentation to the AI coding agents developers already use day-to-day— that's the design. The agent follows those instructions to carry out the actual code conversion.

3Three migration tasks the AI Toolkit handles for you

R → P

① React → Preact conversion

Handles converting legacy React extensions to a Preact-based setup.

② Legacy → Polaris replacement

Maps legacy components to Polaris Web Components and replaces them.

③ Extension API updates

Updates the APIs used by extensions to match the new version.

The targets are Checkout UI extensionsand Customer account UI extensions. As these are upgraded to the new API version, the migration to Polaris Web Components takes place.

4Why the migration is "required": the 2026-10-01 deadline

Shopify CLI blocks updates to apps that contain extensions onan API version older than 1 year.

ItemDetails
Deadline October 1, 2026 Required for any "future app updates" on or after this date
What gets blocked Apps whose Checkout / Customer account UI extensions are on API version 2025-07 or earlier
What happens The affected apps cannot be updated(Shopify CLI blocks the update)
Resolution line Update to API version 2025-10 or later(2025-10 and later default to Polaris Web Components)
Before 2025-07 Legacy (migration required) 2025-10 and later Polaris default = safe zone 2026-10-01 Deadline / update block
To avoid the risk of your app becoming "un-updatable" after the deadline,upgrade to the latest API version now and adopt Polaris Web Components— this is the recommended approach.

5Why Polaris Web Components

Dramatically faster rendering

Extensions built with Polaris Web Components renderdramatically fasterthan legacy React extensions. Load times and extension performance are optimized.

Default from 2025-10 onward

From API version 2025-10 onward, Polaris Web Components are used by default everywhere. Upgrading to the latest version itself moves you toward Polaris.

6Getting started (3 steps)

1

Install the AI Toolkit

Install the Shopify AI Toolkit.

2

Follow the developer documentation

Refer to the migration dev docs (the Checkout and Customer account docs).

3

Run the skill with your AI agent

Run the migration skill on the AI agent you use.

There are two reference docs: Checkout UI extension migration doc and Customer account UI extension migration doc. Choose between them based on the extension types your app has.

75 key points for engineers

Deadline

1. 2026-10-01 is the hard line

After this date, apps containing Checkout / Customer account UI extensions on API version 2025-07 or earlier can no longer be updated. Put it off, and future updates themselves will stop.

CLI BLOCK

2. The block follows a "1-year rule"

Shopify CLI blocks updates to apps containing extensions on an API version older than 1 year. Note that the deadline isn't a fixed date but is determined by how old the version is.

3. Migration happens in three layers

React→Preact, the legacy→Polaris Web Components component swap, and extension API updates. It's not just a dependency version bump — it involves rebuilding the rendering foundation and components.

4. The deadline isn't the only reason to upgrade

Polaris Web Components extensions render dramatically faster than legacy React extensions. Improved load times and performance are another tangible benefit of migrating.

5. You can delegate to AI, but "review stays human"

The AI Toolkit plus the docs feed the migration steps to the agent, but validating the conversion results is the developer's job. The articledoes not statethe accuracy or success guarantees of automated migration, nor the specific names of target APIs or supported agents — so it's safest to proceed on the assumption of hands-on testing.

83 use cases you can apply to your work

Before After
USE CASE 1

Complete the pre-deadline "extension inventory & bulk migration" with minimal effort

Challenge
Your own and your clients' apps have multiple Checkout / Customer account UI extensions, and you can't tell which ones predate API 2025-07—while the 2026-10-01 update block looms.
Approach
Identify the affected extensions, hand the AI Toolkit plus the migration dev docs to an AI agent, and run React→Preact, Polaris replacement, and API updates in sequence.
Impact
Cut manual migration effort while ensuring everything is "update-ready" by the deadline. Resolve delivery risk ahead of schedule.
Technical notes
After migration, always verify on a real environment that the API version is 2025-10 or later and that updates pass via the CLI.
Rendering speed
USE CASE 2

Speed up the checkout experience "while you're at it" with the migration

Challenge
Legacy React extensions make checkout slow to load, raising concerns for UX and conversion—but it's hard to justify the effort for improvements on their own.
Approach
Migrate to Polaris Web Components at the same time as the deadline-driven migration, folding rendering performance gains into the same work.
Impact
Bundle the "mandatory compliance (deadline)" and "performance improvement (UX)" into a single migration, making the ROI easier to explain.
Technical notes
Measure load times before and after migration; capturing the Polaris benefit as numbers makes it reusable in proposal materials.
USE CASE 3

Build an in-house "playbook" for running AI coding agents

Challenge
You want to bring AI coding agents into development, but their scope is vague and you haven't defined concrete tasks that deliver results.
Approach
Start with a well-defined task that has an official skill and documentation—"Polaris migration of extensions"—and establish an agent operations flow (run → review → verify) in-house.
Impact
Because the task has a clear goal and an official procedure, you can accumulate AI success stories and operational know-how at low risk.
Technical notes
You're free to use "whatever AI agent you prefer." Use this as a chance to verify how well it works with your in-house standard agent.

9A one-line summary you can use in proposals

"An official skill that hands off the Polaris Web Components migration of Checkout / Customer account UI extensions to an AI agentAutomates
React→Preact conversion, component replacement, and API updates—while also speeding up rendering.
From 2026-10-01, apps on API 2025-07 or earlier can no longer be updated,so migrating early is the safe move."