Streaming to a UI¶

The package has no event format of its own. Everything your UI needs arrives as standard ADK Event objects from runner.run_async(), so any ADK client or protocol adapter, such as one for AG-UI or CopilotKit, works unchanged.

Reading an event¶

What to show	Where it is in the event
Assistant text	`part.text` where `part.thought` is false
Reasoning	`part.text` where `part.thought` is true (needs `include_thoughts=True`)
Tool call started	`event.get_function_calls()`: name, args, id
Tool result	`event.get_function_responses()`: name, response, id
Which agent	`event.author`: the root's name or a subagent's
Which delegation	`event.branch`, for example `editor.reviewer@<call-id>`
A question for the user	`project_elicitation_event(event)` is not `None` (see Asking the user)
Token usage	`event.usage_metadata`: prompt, output, reasoning, and cached token counts
Streaming chunk	`event.partial` is true (with `RunConfig(streaming_mode=StreamingMode.SSE)`)

These map onto AG-UI's text message, reasoning, tool call, and tool call result events.

Subagent activity¶

Prebuilt and foreground spawned subagents stream inside the root stream, in order, between the root's tool call and its tool result:

author=editor    call   reviewer(request=…)        ← root delegates
author=reviewer  call   search_sources(…)          ← child's tool call
author=reviewer  result search_sources             ← child's tool result
author=reviewer  thought …                         ← child's reasoning
author=reviewer  text   "Two claims need sources…" ← child's answer
author=editor    result reviewer                   ← back to the root
author=editor    text   "Revised report: …"

To group a child's events in the UI, use event.author, or event.branch to tell two calls to the same child apart. The call ID in the branch matches the root's tool call that started the child.

Background subagents are the exception: their events come from stream_background_task_events(task_id), a separate stream you can forward on its own channel.

Minimal example¶

async for event in runner.run_async(user_id=uid, session_id=sid, new_message=msg):
    who = event.author
    for call in event.get_function_calls():
        ui.tool_started(who, call.id, call.name, call.args)
    for response in event.get_function_responses():
        ui.tool_finished(who, response.id, response.name, response.response)
    for part in event.content.parts if event.content else []:
        if part.text:
            (ui.reasoning if part.thought else ui.text)(who, part.text)