Create Chat (OpenAI Compatible)

Beta

POST

https://api.vapi.ai/chat/responses

Authentication

AuthorizationBearer

Authenticate server-side requests with a private Vapi API key. Create or copy a key from the Vapi Dashboard and send it in the Authorization header as Bearer <token>. Keep private API keys out of client-side code and public repositories.

Request

This endpoint expects an object.

inputstring or list of objectsRequired

This is the input text for the chat. Can be a string or an array of chat messages. This field is REQUIRED for chat creation.

assistantIdstringOptional

This is the assistant that will be used for the chat. To use an existing assistant, use assistantId instead.

assistantobjectOptional

This is the assistant that will be used for the chat. To use an existing assistant, use assistantId instead.

assistantOverridesobjectOptional

These are the variable values that will be used to replace template variables in the assistant messages. Only variable substitution is supported in chat contexts - other assistant properties cannot be overridden.

squadIdstringOptional

This is the squad that will be used for the chat. To use a transient squad, use squad instead.

squadobjectOptional

This is the squad that will be used for the chat. To use an existing squad, use squadId instead.

namestringOptional<=40 characters

This is the name of the chat. This is just for your own reference.

sessionIdstringOptional

This is the ID of the session that will be used for the chat. Mutually exclusive with previousChatId.

streambooleanOptionalDefaults to true

Whether to stream the response or not.

previousChatIdstringOptional

This is the ID of the chat that will be used as context for the new chat. The messages from the previous chat will be used as context. Mutually exclusive with sessionId.

transportobjectOptional

This is used to send the chat through a transport like SMS. If transport.phoneNumberId and transport.customer are provided, creates a new session. If sessionId is provided without transport fields, uses existing session data. Cannot specify both sessionId and transport fields (phoneNumberId/customer) together.

Response

OpenAI Responses API format - either non-streaming or streaming

ResponseObjectobject

ResponseTextDeltaEventobject

ResponseTextDoneEventobject

ResponseCompletedEventobject

ResponseErrorEventobject