The JSON Liquid filter will no longer output the inventory_quantity and inventory_policy fields
API
Effective December 05, 2017
As of December 5, 2017, inventory_quantity and inventory_policy fields accessed through a JSON Liquid filter are deprecated. The JSON filter will not output those fields for shops created after that date.
If you want to consume inventory information about a product, you can leverage variant.inventory_quantity and variant.inventory_policy. We recommend using that information behind a setting that the merchant has to turn on. This is a part of our efforts which kickstarted last year to eliminate bots and crawlers from knowing inventory levels of products from stores that they haven't explicitly been granted access to. Themes in the Shopify Theme Store will be updated before December 5, 2017.