feat: Add model parameter to RealtimeAgent class

[pxkundu]

Summary

This PR adds a model parameter to the RealtimeAgent class, enabling different agents to use different models based on their specific requirements. This addresses issue #1888 which requested the ability to set up smarter models for agents with specific tasks.

Key changes:

• Added optional model parameter to RealtimeAgent class
• Updated session logic to use agent-specific model when specified
• Agent's model overrides default configuration from RealtimeRunner
• Backward compatible - agents without model parameter work as before

Use case example:

# Use a smarter model for complex analysis tasks
analysis_agent = RealtimeAgent(
    name="Analysis Agent",
    instructions="Perform complex data analysis",
    model="gpt-4o-realtime-preview"  # Smarter model
)

# Use default or lighter model for simple greetings
greeting_agent = RealtimeAgent(
    name="Greeting Agent",
    instructions="Welcome users",
    model="gpt-realtime"  # Default model
)

Test plan

1. Unit tests (tests/realtime/test_agent.py):

   • ✅ Test agent initialization with model parameter
   • ✅ Test model parameter in clone() method

2. Integration tests (tests/realtime/test_agent_model.py):

   • ✅ Test agent's model is used in session configuration
   • ✅ Test agent without model uses default from run config
   • ✅ Test agent's model overrides default configuration
   • ✅ Test agent update with different model

3. Quality checks:

   • ✅ make format - all files formatted
   • ✅ make lint - no linting errors
   • ✅ mypy - type checking passes
   • ✅ All 8 new tests pass

Issue number

Closes #1888

Checks

• I've added new tests (if relevant) - Added 8 comprehensive tests
• I've added/updated the relevant documentation - Updated docstring in RealtimeAgent class
• I've run make lint and make format - All checks pass
• I've made sure tests pass - All tests pass (8/8 new tests)

Implementation Details

Files Changed:

1. src/agents/realtime/agent.py:

   • Added model: str | None = None parameter
   • Updated class docstring to remove statement that model isn't supported
   • Added comprehensive documentation for the new parameter

2. src/agents/realtime/session.py:

   • Modified _get_updated_model_settings_from_agent() to use agent's model
   • Agent's model is set in model_name field of session settings
   • Maintains proper precedence: agent model > run config > defaults

3. tests/realtime/test_agent.py:

   • Added test_agent_model_parameter() - tests basic parameter functionality
   • Added test_agent_model_clone() - tests model preservation in cloning

4. tests/realtime/test_agent_model.py (new file):

   • Comprehensive integration tests with mock model
   • Tests session configuration with agent model
   • Tests default behavior and overrides
   • Tests agent handoffs with different models

Backward Compatibility

✅ Fully backward compatible

• Agents without model parameter work exactly as before
• Default behavior unchanged when model is not specified
• Existing code continues to work without modifications

Related Discussion

This feature was requested in issue #1888 and approved by maintainer @seratch who said:

"Indeed, enabling to pass the model name to realtime agents could be more intuitive but the current design accepts the model name on the RealtimeRunner side. So, please go ahead with it."

The implementation follows the approved approach while maintaining consistency with the existing architecture.

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[chatgpt-codex-connector]

Agent-specific model ignored when session starts

The new block assigns updated_settings["model_name"] = agent.model, but a few lines later the method calls updated_settings.update(starting_settings) when __aenter__ builds the initial model_config. Because starting_settings typically contains the default model name, the assignment here is overwritten and the initial session still uses the runner’s default model. The new model parameter therefore only takes effect after an explicit update_agent() call and fails for the very first agent—the main scenario called out in the summary. Consider applying starting_settings before writing the agent override or omitting the extra update to preserve the intended precedence of agent > run config > defaults.

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[seratch]

Hi @pxkundu, thanks for sending this PR, but I didn't mean we'd immediately add this option to realtime agents. We may not accept the suggested changes at this moment.

[pxkundu]

Thank you @chatgpt-codex-connector for catching that P1 bug! You're absolutely right - the agent's model was being overridden by starting_settings.

Fixed in commit 0c8c00a:

• Moved agent model assignment to occur after starting_settings.update()
• This ensures proper precedence: agent.model > starting_settings > run_config > defaults
• Added a specific test (test_agent_model_not_overridden_by_starting_settings) to verify this scenario

The fix ensures the agent's model is respected from the very first session start, not just after update_agent() calls.

---

@seratch - Thank you for the feedback. I apologize if I misunderstood the intent of your comment in #1888.

When you said "please go ahead with it," I interpreted that as approval to implement the feature. I understand now that you may have meant to explore the idea further before committing to it.

Questions for clarification:

1. Are there specific concerns about this approach that I should address?
2. Is there a different design you'd prefer to explore?
3. Would you like me to close this PR, or keep it open for future consideration?

I'm happy to:

• Make any adjustments to align with your vision
• Close this PR if the timing isn't right
• Wait for further discussion before proceeding

Thank you for your guidance!

[chatgpt-codex-connector]

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[seratch]

When you said "please go ahead with it," I interpreted that as approval to implement the feature. I understand now that you may have meant to explore the idea further before committing to it.

I meant the author of the issue can pass a model name to the runner for now.

Regarding your suggestion here, we actually don't need the change in the short term. So, let us close this PR now. If you're looking for anything to contribute to this project, fixing practical bugs rather than nice-to-have changes would be helpful to us. Thanks again for your interest.

[pxkundu]

Thank you for the clarification @seratch! I misunderstood the initial comment - I see now that you meant the issue author could pass the model name to the runner (which already exists), not to add it to the agent level.

I appreciate your guidance about focusing on practical bugs rather than nice-to-have features. That's very helpful feedback for future contributions.

Thanks for your time and patience!