Does Hyvä work with my custom checkout extension?

Depends on which checkout you’re running and which extension. Three cases:

• You’re replacing default Magento checkout with Hyvä Checkout (recommended). Hyvä Checkout has a defined plugin interface for shipping methods, payment methods, and custom fields. Klarna, Stripe, Adyen, Mollie, Affirm, PayPal Braintree, Authorize.net all have working Hyvä Checkout adaptors. Custom checkout extensions need re-implementing as Magewire components, the calculator’s 1.4x “custom checkout” multiplier funds this.
• You’re keeping default Magento Luma checkout and only porting the storefront to Hyvä. Works fine but you don’t get the perf lift on checkout pages (the biggest conversion-lift surface). I do this for ~10% of migrations, usually B2B stores with a one-off legacy checkout integration that’s too expensive to port.
• You’re running OneStepCheckout / Magezon Checkout / Aheadworks One Step Checkout. These don’t port to Hyvä Checkout, the extension vendor has to ship a Hyvä Checkout version (only OneStepCheckout has, as of mid-2026). Path forward: drop the third-party checkout extension and use Hyvä Checkout directly.

I audit your specific checkout shape in step 1 (Audit Luma). The audit output tells you which of the three buckets you’re in.