Call Stages
The Ultravox API’s Call Stages functionality allows you to create dynamic, multi-stage conversations. Stages enable more complex and nuanced agent interactions, giving you fine-grained control over the conversation flow.
Each stage can have a new system prompt, a different set of tools, a new voice, an updated conversation history, and more.
Understanding Call Stages
Call Stages (“Stages”) provide a way to segment a conversation into distinct phases, each with its own system prompt and potentially different parameters. This enables interactions that can adapt and change focus as the conversation progresses.
Key points to understand about Stages:
Dynamic System Prompts → Stages allow you to give granular system prompts to the model as the conversation progresses.
Flexibility → You have full control to determine when and how you want the conversation to progress to the next stage.
Thoughtful Design → Implementing stages requires careful planning and consideration of the conversation structure. Consider how to handle stage transitions and test thoroughly to ensure a natural flow to the conversation.
Maintain Context → Think about how the agent will maintain context about the user between stages if you need to ensure a coherent conversation.
Creating and Managing Stages
To implement Call Stages in your Ultravox application, follow these steps:
1. Plan Your Stages
Determine the different phases of your conversation and what prompts or parameters should change at each stage.
2. Implement a Stage Change Tool
Create a custom tool that will trigger stage changes when called. This tool should:
- Respond with a
new-stage
response type. This creates the new stage. How you send the response depends on the tool type:- For server/HTTP tools, set the
X-Ultravox-Response-Type
header tonew-stage
. - For client tools, set
responseType="new-stage"
on yourClientToolResult
object.
- For server/HTTP tools, set the
- Provide the updated parameters (e.g., system prompt, tools, voice) for the new stage in the response body.
Unless overridden, stages inherit all properties of the existing call. See Stages Call Properties for the list of call properties that can be changed.
3. Configure Stage Transitions
- Prompt the agent to use the stage change tool at appropriate points in the conversation.
- Ensure the stage change tool is part of
selectedTools
when creating the call as well as during new stages (if needed). - Update your system prompt as needed to instruct the agent on when/how to use the stage change tool.
Example Stage Change Implementation
Here’s a basic example of how to implement a new call stage.
First, we create a tool that is responsible for changing stages:
We also need to ensure that we have instructed our agent to use the tool and that we add the tool to our selectedTools
during the creation of the call.
Ultravox API Implications
If you are not using stages for a call, retrieving calls or call messages via the API (e.g. GET /api/calls
) works as expected.
However, if you are using call stages then you most likely want to use the stage-centric API endpoints to get stage-specific settings, messages, etc.
Use GET /api/calls/{call_id}/stages
to get all the stages for a given call.
Ultravox API | Description | Stage-Centric Equivalent | Description |
---|---|---|---|
/calls/{call_id} | Get a call | /calls/{call_id}/stages/{call_stage_id} | Get the call stage |
/calls/{call_id}/messages | Get messages for a call | /calls/{call_id}/stages/{call_stage_id}/messages | Get message for the stage |
/calls/{call_id}/tools | Get tools for a call | /calls/{call_id}/stages/{call_stage_id}/tools | Get tools for the stage |
Stages Call Properties
Unless overridden, stages inherit all properties of the existing call.
Here is the list of all call properties that can and cannot be changed during a new stage:
property | change with new stage? |
---|---|
systemPrompt | Yes |
temperature | Yes |
voice | Yes |
languageHint | Yes |
initialMessages | Yes |
selectedTools | Yes |
firstSpeaker | No |
model | No |
joinTimeout | No |
maxDuration | No |
timeExceededMessage | No |
inactivityMessages | No |
medium | No |
recordingEnabled | No |
Use Cases for Call Stages
Call Stages are particularly useful for complex conversational flows. Here are some example scenarios:
Data Gathering → Scenarios where the agent needs to collect a lot of data. Examples: job applications, medical intake forms, applying for a mortgage.
Here are potential stages for a Mortgage Application:
- Stage 1: Greeting and basic information gathering
- Stage 2: Financial assessment
- Stage 3: Property evaluation
- Stage 4: Presentation of loan options
- Stage 5: Hand-off to loan officer
Switching Contexts → Scenarios where the agent needs to navigate different contexts. Examples: customer support escalation, triaging IT issues.
Let’s consider what the potential stages might be for Customer Support:
- Stage 1: Initial greeting and problem identification
- Stage 2: Troubleshooting
- Stage 3: Resolution or escalation (to another stage or to a human support agent)
Conclusion
Call Stages in the Ultravox API give you the ability to create adaptive conversations for more complex scenarios like data gathering or switching contexts. By allowing granular control over system prompts and conversation parameters at different stages, you can create more dynamic and context-aware interactions.