When this article first ran in early 2023, checkout extensibility was the new thing you'd eventually migrate to. That's over: checkout.liquid was retired across 2024–2025, and extensibility is simply how Shopify checkout works now. Here are the five things worth knowing in 2026 — rewritten from experience building on it, not from the launch announcement.
You don't edit checkout markup anymore — on any plan. You attach checkout UI extensions (React components) at defined slots: above the order summary, after the address, before payment, on the thank-you page. Shopify owns the frame; your code owns the slots. The trade is real: less arbitrary control than the checkout.liquid era, in exchange for customizations that survive every checkout update Shopify makes.
Customizing the checkout itself — in-checkout UI extensions, payment and delivery customizations — is part of the Shopify Plus offer. Non-Plus stores get the surrounding surfaces: cart, post-purchase, thank-you, order status. If checkout control is the reason you're weighing Plus, it's one of the honest reasons on the list.
From real engagements: B2B fields that validate against an ERP before the order exists, delivery instructions that flow to the carrier, hiding installment options on orders over a threshold, gift messaging that prints on the packing slip, address validation that stops a bad ZIP before it becomes a support ticket. The pattern — move the check to the moment the customer can still fix it.
The 2023 worry was that giving up checkout.liquid control would cost conversion levers. In practice the opposite held: extensibility checkouts stay fast because no one can inject a 300KB script tag into the payment page, and Shop Pay sits natively on top. The levers that matter — fewer fields, validation before submit, the right payment options per customer — are all expressible with extensions and Functions.
Field validation, gated payment methods, B2B rules, upsells that don't embarrass the brand — email Tom what the checkout should do.
Email Tom →