Python: [Bug]: WorkflowAgent incompatible with add_agent_framework_fastapi_endpoint - streaming interface mismatch

[gerardogreco-psen]

Description

Hi! I think there is an incompatibility between WorkflowAgent (returned by Workflow.as_agent()) and the add_agent_framework_fastapi_endpoint function from agent_framework_ag_ui.

When trying to expose a workflow through the AG-UI endpoint, the application crashes at runtime with a TypeError because the AG-UI code attempts to await an async generator, which is not a valid operation.

This prevents users from exposing multi-agent workflows (created for example with GroupChatBuilder) through FastAPI endpoints using the standard AG-UI integration.

Code Sample

from agent_framework_ag_ui import add_agent_framework_fastapi_endpoint
from agent_framework_orchestrations import GroupChatBuilder
from agent_framework import Agent
from agent_framework.openai import OpenAIChatClient
from fastapi import FastAPI

# Create agents
def create_openai_client() -> OpenAIChatClient:
    return OpenAIChatClient(
        base_url="https://example.openai.azure.com/openai/v1/",
        api_key="your-api-key",
        model_id="gpt-4",
    )

triage_agent = Agent(
    client=create_openai_client(),
    instructions="You are a triage agent",
    name="triage_agent",
    description="Routes requests",
    tools=[],
)

specialist_agent = Agent(
    client=create_openai_client(),
    instructions="You are a specialist",
    name="specialist_agent",
    description="Handles specialized requests",
    tools=[],
)

# Create workflow
workflow = GroupChatBuilder(
    participants=[specialist_agent],
    orchestrator_agent=triage_agent
).build()

# Try to expose workflow through AG-UI endpoint
app = FastAPI()
workflow_agent = workflow.as_agent()
add_agent_framework_fastapi_endpoint(app=app, agent=workflow_agent, path="/chat")

# This will crash at runtime when a request is made to the endpoint

Error Messages / Stack Traces

TypeError: object async_generator can't be used in 'await' expression

Traceback (most recent call last):
  File "venv\Lib\site-packages\agent_framework_ag_ui\_agent.py", line 116, in run_agent
    async for event in run_agent_stream(input_data, self.agent, self.config):
        yield event
  File "venv\Lib\site-packages\agent_framework_ag_ui\_run.py", line 877, in run_agent_stream
    stream = await cast(Awaitable[ResponseStream[Any, Any]], response_stream)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: object async_generator can't be used in 'await' expression

Package Versions

python-1.0.0b260210

Python Version

Python 3.13.3

Additional Context

Root cause location - Analyze by AI (agent_framework_ag_ui/_run.py:873-877):

response_stream = agent.run(messages, stream=True, **run_kwargs)
if isinstance(response_stream, ResponseStream):
    stream = response_stream
else:
    stream = await cast(Awaitable[ResponseStream[Any, Any]], response_stream)
    # ^ This fails because WorkflowAgent.run(stream=True) returns AsyncIterable, not Awaitable[ResponseStream]

[moonbox3]

We have pending work to support native workflows with AG-UI.

[moonbox3]

Also it looks like this behavior changed as of #3379. Will need to look into it.

[mihail-monaco]

Thanks for the response @moonbox3! Do you have a sense for when that native AG-UI support is expected to be landed? Would help us with some planning efforts.

[moonbox3]

Thanks for the response @moonbox3! Do you have a sense for when that native AG-UI support is expected to be landed? Would help us with some planning efforts.

@mihail-monaco, we're doing some planning so will have some more to share in a week or two. I'll post back here if I have any updates sooner.

[moonbox3]

With that said, this looks like a regression because at one point it did work to turn a workflow into an agent and run it in ag-ui. I will have a look at that part.

[mihail-monaco]

thank you!