All Release NotesCustom line items behavior improved6 October 2017HTTP APIEnhancementCarts The behavior of CustomLineItems has been improved to behave more similar to regular LineItems when signing in, and when adding a new item. [API] When a customer signs in and the default anonymousCartSignInMode is used, custom line items are merged into the existing customer's cart. [API] When a custom line item is added and an equivalent one already exists in the cart, the quantity is increased.