This functionality is in Limited Availability. We are actively soliciting feedback from a small set of early adopters.
The CPQ X API is a set of global classes that provide a way to create Apex representations of the data in QuoteRatePlan, QuoteAmendment, QuoteRatePlanCharge, and QuoteChargeTier objects. You do not need to directly manage the states of these objects when using the CPQ X global classes.
These global classes fall into two categories: CPQ X Models and CPQ X Utilities. The CPQ X Model classes are a set of data model classes and the CPQ X Utility classes provide a set of APIs that enable you to build, read, and save the CPQ X objects.