What changed
On September 15, 2026, Shopify made API version 2026-10 available as a release candidate for development testing; it becomes stable October 1. The release notes consolidate several action-required or behavior-changing migrations. Updating an unfulfilled order’s shipping address now recalculates taxes for the new destination. Deprecated `priceRule` data is removed from draft-order discount warnings and legacy `PriceRule` types are removed from the public schema. Customer Account API removes `Customer.lastIncompleteCheckout` and its unreachable `Checkout` subtree. Creating a carrier service no longer adds rates to the General shipping profile automatically. Tax-app webhook payloads also move to newer identifier semantics. Shopify recommends reviewing and adjusting affected integrations before adopting 2026-10.
Why it matters
Quarterly API versions can look like housekeeping, but this RC contains changes that affect money movement, checkout visibility and schema compatibility. An app that edits order addresses may now create payment/refund differences after tax recalculation; a shipping integration can successfully register a carrier service without making its rates visible at checkout; and stale GraphQL queries can fail when removed fields disappear. The release-candidate period is therefore the practical migration window, not merely an announcement before October.
Order-address edits can now change the financial state of an order
When an app updates the shipping address of an unfulfilled order, Shopify recalculates taxes for the new destination. Integrations that previously treated the address update as a mostly logistical mutation need to fetch updated tax lines and totals and handle any resulting amount due or refund balance.
Removed draft-order fields create a hard GraphQL compatibility boundary
Queries that still select `priceRule` from `DraftOrderDiscountNotAppliedWarning` or depend on the legacy `PriceRule` types need to migrate to newer discount title/code fields. Because the fields are removed from the public 2026-10 schema, this is not merely a deprecation warning once the app adopts the version.
Carrier service creation no longer implies checkout visibility
Registering a carrier service through GraphQL or REST now creates the service without automatically adding its rates to the General shipping profile. Apps and setup workflows must explicitly configure carrier-calculated rates in the appropriate profile.
Customer-account integrations need to remove dead checkout queries
The Customer Account API drops `Customer.lastIncompleteCheckout` and its nested `Checkout` types. Shopify says there is no Customer Account API replacement, so affected apps need to remove that dependency rather than simply rename a field.
The RC is the safest place to find these failures
Shopify marks release candidates for development rather than production. Testing now lets apps catch schema errors and behavioral differences before October 1, while supported stable versions remain available during the migration.