Allow us to call on a custom Assistant using Assistant API instead of only the base model GPT. This will allow us to leverage RAG and function calling and especially Thread ID, so we can have consistency across multiple conversations with the same customer.

Alternatively, introduce an equivalent to Thread ID so we can achieve the same consistently natively with VAPI. The use case for clarity is the ability to save the ThreadID to the customer contact in the CRM and then recall it on every subsequent conversation.