Verified facts
What happened
On API version 2026-10, Shopify Functions can query metafields on options in cart.deliveryGroups.deliveryOptions.
The returned metafield can expose its value, type, and jsonValue, but the data is not persisted after checkout.
Delivery option generator functions and shipping carrier service responses can attach the data; downstream Delivery Customization Functions can then read app-reserved or unprefixed shared namespaces.
The field is available wherever the Functions input includes delivery options, while legacy Order Discounts and Product Discounts APIs have empty cart.deliveryGroups and therefore return no value.
Business relevance