The Product Variant resource has new defaults for inventory_quantity and inventory_management
API
Effective October 10, 2018
When you create a new product variant, there are two new default values applied to the inventory_quantity and inventory_management properties.
inventory_quantitynow defaults to0inventory_managementnow defaults toshopify
The change to inventory_quantity is live, and the change to inventory_management will come next week.
To learn more, see Product Variant.