AssistantsGPT-Live

GPT-Live quickstart

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Make a first call and see how the speaker and reasoner work together

This quickstart creates a simple front-desk assistant and makes a browser call to it. It needs no server of your own. It uses one built-in tool, endCall, so you can see a delegation happen and find it in the call record.

Before you start

  • GPT-Live enabled for your Vapi organization. See access.
  • A browser with a microphone.
  • For the API path, a Vapi private API key.
  • If you use your own OpenAI API key, it needs access to GPT-Live and to the reasoner model. This quickstart uses the default, gpt-5.6-terra.

Create the assistant

The assistant answers for Example Service Studio, a fictional business. It greets the caller, asks for their name and reason for calling, and ends the call when they’re done. It has two prompts: the speaker prompt shapes the conversation, and the reasoner prompt handles tasks, which here is only ending the call.

1

Create an assistant

Open Assistants and select Create Assistant. This creates a new Classic assistant.

2

Switch it to GPT-Live

On the new assistant, select Try GPT Live, then confirm with Switch to GPT Live. The switch publishes the assistant, so don’t attach a phone number until you’ve finished testing. When the conversion completes, choose Marin as the voice.

3

Set the prompts

In Speaker, enter:

Speaker instructions
You are the front desk for Example Service Studio, a fictional business used
for testing. Greet callers warmly, ask for their name and the reason for their
call, and summarize what they told you. You can't look anything up or book
appointments yet, so say so if they ask.
Speak plainly and keep replies short. Ask one question at a time. Use details
the caller has already given.
Delegation policy:
Backend tools:
- Ending the call.
Delegate to the backend when:
- The caller asks to end the call or says goodbye. Always delegate this.
  Saying goodbye does not end the call.

In Reasoner, enter:

Reasoner instructions
Call endCall when the caller asks to end the call or says goodbye.
4

Add the end-call tool

Add the built-in End Call tool to the assistant.

5

Set the greeting and publish

Set the first message to “Hi, this is Example Service Studio. Who am I speaking with?” and set the assistant to speak first. Select Publish.

Talk to it

Open the assistant in the dashboard and select Talk. Allow microphone access. Try these, one at a time:

  1. Give several details at once. “Hi, it’s Sam, I’m calling about moving my appointment.” The assistant should use both and not ask for your name again.
  2. Interrupt it. Start speaking while it’s talking. It should stop and listen.
  3. Change the pace. “Could you slow down a little?” It should adjust.
  4. Say goodbye. “Thanks, that’s everything. Bye.” The call should end.

The greeting and replies are generated, so the wording varies from call to call and may not match your first message exactly. The assistant may also be cut off before it finishes saying goodbye, because ending the call is an action that happens as soon as the reasoner takes it.

Check what happened

Open the call in Call Logs. You’ll find:

  • The transcript of both sides of the conversation.
  • The recording, if recording is enabled.
  • An endCall tool call in the call’s messages. This is the reasoner acting on the speaker’s delegation.
  • The ended reason, which shows that the assistant ended the call.

That endCall entry is the thing to look for. The assistant saying “goodbye” and the call actually ending are separate events, so check for the action as well as the words.

If the call didn’t end

If the assistant said goodbye but the call stayed open, look in the call’s messages for an endCall tool call:

  • No endCall entry. The speaker may not have delegated, or the reasoner may not have called the tool. Check that the speaker prompt lists ending the call as a delegation trigger, the reasoner prompt says to call endCall, and the tool is attached. Delegation is a model decision, so try a few calls.
  • An endCall entry is there. The delegation happened, so look at the tool’s result for an error.

See the troubleshooting guide for more checks.

Next steps