Shopify says its migration of five Checkout Blocks extensions to Polaris web components cut transferred bundle sizes by 40.5% to 84.4% and improved checkout-volume-weighted Extension Load Time (ELT) by 8% at P50 and 7% at P90. Those are Shopify’s reported results from its own production upgrade—not an independent benchmark or a guarantee that another extension will see the same gains.
What Shopify changed
The five high-traffic Checkout Blocks extensions had used React, Shopify’s legacy Remote UI bridge, and API version 2025-07. Shopify moved them to API version 2026-01, remote-dom, Preact, and Polaris web components, while also rewriting the codebase in TypeScript. The shared code was reorganized from extensions/core to extensions/core-next, alongside changes to markdown, Liquid parsing, and date utilities. Shopify describes the implementation in its July 16, 2026 engineering case study.
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How the rendering model differs
In Shopify’s explanation, remote-dom mirrors DOM nodes from an extension’s sandbox to the host. The legacy approach used React’s reconciler to translate a React tree into the Remote UI serialized protocol. Shopify chose Preact to preserve a React-like hooks model with a smaller framework footprint, and replaced the Polaris React component tree with Polaris web components.
How much smaller the bundles became
Shopify reported the following reductions in transferred bundle size for the five extensions. The percentages are the company’s production figures, not results from a third-party test.
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- Compatible with: ✅Shopify POS on Android ✅Shopify POS on iPad
- The receipt printer can connect to your tablet via Bluetooth or Ethernet (via router)
- The Cash drawer connects directly to the receipt printer with the included RJ11 cable.
- The Thermal Printer does not require ink or toner. (Thermal paper roll required - 80mm or 3-1/8 inches paper width).
- PRINTER SETUP: In Shopify POS, tap Settings>Set up a new device > Receipt printers, and follow the prompts. (The Cash drawer connects directly to the receipt printer with the included RJ11 cable, no setup required) SCANNER SETUP: 1- In the included manual, scan Bluetooth HID mode. 2-On your device, Search for Bluetooth devices, and pair. 3-In Shopify POS app, go the Settings, and enable "Allow HID mode" 4-Android only- On device, go to Settings > System > Keyboard > Physical keyboard and turn on "Show on-screen keyboard"
| Extension | Reported transferred bundle reduction |
|---|---|
| Payment icons | 84.4% |
| Static content | 54.1% |
| Custom field | 44.6% |
| Dynamic content | 45.2% |
| Line-item actions | 40.5% |
Across the family, Shopify summarized the reduction as 40% to 85%. The broad range reflects differences between extensions; it should not be read as a predicted saving for every Shopify checkout extension.
What Shopify says drove the reduction
For this migration, Shopify’s 2026-01 remote-dom CLI imposed a 64 KB gzip limit per extension bundle. Before the upgrade, the extensions were 300–356 KB raw, or about 100–112 KB gzipped, according to Shopify. Moving to Preact removed react-reconciler, which Shopify estimates at approximately 89 KB. The team also replaced liquidjs—approximately 73 KB in the article—with a smaller in-house Liquid parser called “droplet.” Shopify needed to retain Liquid support because merchants can write Liquid in block configurations while staying within the bundle budget.
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- Compatible with: ✅Shopify POS on Android ✅Shopify POS on iPad
- The receipt printer can connect to your tablet via Bluetooth or Ethernet (via router)
- The Cash drawer connects directly to the receipt printer with the included RJ11 cable.
- The Thermal Printer does not require ink or toner. (Thermal paper roll required - 80mm or 3-1/8 inches paper width).
- SETUP: In Shopify POS, tap Settings>Set up a new device > Receipt printers, and follow the prompts. (The Cash drawer connects directly to the receipt printer with the included RJ11 cable, no setup required)
How much faster Shopify says they loaded
Shopify defines Extension Load Time (ELT) as the time a single extension takes to load on its own. Across checkout-volume-weighted results, the company reported an 8% improvement at P50 and a 7% improvement at P90. These are relative ELT changes; the case study does not report an absolute number of seconds saved on checkout completion or a conversion-rate increase.
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|---|---|---|
| Dynamic content | -8.2% | -7.9% |
| Line-item actions | -8.4% | -6.5% |
| Custom field | -8.1% | -5.9% |
| Static content | -6.5% | -3.8% |
| Payment icons | -11.7% | -11.9% |
The extension-level figures and the weighted family result answer different questions: an individual extension’s change need not match the overall weighted improvement. Shopify published these as production measurements; the cited material does not provide an independent replication or controlled third-party benchmark.
What the API versions mean for developers
Shopify’s Checkout UI extension documentation identifies API version 2025-07 as the final version supporting React-based UI components. The migration guide says extensions on versions earlier than 2025-10 must adopt Polaris web components, while versions 2025-10 and later use them by default. See Shopify’s 2025-07 Checkout UI extension documentation and migration guide.
The 2025-07 documentation stated that, starting October 1, 2026, app deployments would be blocked if they included extension versions earlier than 2026-01. That date has passed. Because deployment enforcement and version rules can change, check the current Shopify developer guidance before planning a release rather than assuming the historical notice still describes live enforcement.
Rank #4
- Highly flexible - The 360° rotatable base and tablet bracket holder combined with a folding arm offer unparalleled adjustment for typing or showcasing without missing any viewing angles. Turn display in a second between cashier and shopper or switch landscape/portrait mode instantly.
- Business-oriented - Two size rubber padded bracket holders collectively fit 6" - 13" tablets or any gadgets with width or height measurement in the range of 6.6"-9.6" (Please noticed that both two clips fit cases less than 0.5" thickness), An ideal docking station stand for perfect match of large or small tablet pcs typically used at restaurant shop point of sale, office home desk, etc.
- Ergonomic design - Quick attach/detach of holder with simple push of the button creates no hassle for easy storage and carrying. A true universal ipad kiosk stand with easy pull handlebar and dedicated space for power cord charging.
- Broad application - Not only does it make your ipads/android/windows surface tablets a desktop display computer, it allows you to type, press, view, swivel with great stability. Confidently interact with customers at restaurant, check out at register, collaborate in group meeting at office, present products or services at showroom, and many more.
- Steady support - Light and smooth turning of bracket holder/arm provides high efficiency in busy settings. The weighted base plus hard folding arm offer sturdy structure to withstand weights of large tablets and heavy operation on the device, a professional grade tablet stand.
Bundle-size limits use different terms
Shopify’s engineering case study describes a 64 KB gzip limit in the context of the 2026-01 remote-dom CLI migration. Separately, Shopify’s current API-version documentation states a maximum compiled bundle size of 64 KB for checkout UI extensions and 128 KB for full-page customer account extensions. “Gzip” in the migration account and “compiled bundle” in the API documentation are not interchangeable labels; verify the current requirements for the API version and extension type you target.
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What Shopify’s rollout suggests about migration risk
Shopify says it rolled out the changes incrementally, releasing at most one extension per day and starting with the lowest-risk extension. It monitored per-extension metrics and reported one rollback after a date-picker collision, which it says was fixed forward the next day. The team also validated Liquid parity against live configuration. These are Shopify’s descriptions of its own rollout, not independent verification of reliability.
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- Includes an Epson USB Thermal Receipt Printer (With Autocut), and The EOM-100 Cash Drawer
- Compatible with Square Stand and Square Register
- 2 Year Full Warranty, Lifetime Tech Support, from EOM-POS
- The receipt printer connects to the USB ports on the Square Stand- No installation required. The Cash Drawer connects with a Built in RJ12/11 cable (included) to the Printer for automatic opening of cash drawer
- The Thermal Printer does not require ink or toner. (Thermal paper roll required - 80mm or 3-1/8 inches paper width).
The company’s stated engineering lessons are practical for teams facing a similar migration:
- Treat a hard bundle limit as a reason to evaluate oversized dependencies, not merely as a target for superficial minification.
- Use production metrics for each extension as rollback signals, rather than relying only on an aggregate result.
- Test against real configuration data as well as synthetic cases, especially where merchants can supply Liquid or other configurable content.
- Use automation or AI for repetitive conversion work, but keep human review for difficult migration decisions.
Shopify’s article puts its view succinctly: “Metrics are your real rollback signal.”
Where Polaris web components fit
Polaris is Shopify’s web-component toolkit for surfaces including Admin, Checkout, and Customer Accounts. Shopify says web components remove React runtime overhead in UI extensions; that platform context explains the direction of the migration but is not an independent performance study. Checkout block examples in Shopify’s documentation include product upsells, trust badges, and loyalty-program displays. Those examples illustrate possible uses and should not be confused with the five extensions in this specific case study.
Quick Recap
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