> ## Documentation Index
> Fetch the complete documentation index at: https://docs.aion.to/llms.txt
> Use this file to discover all available pages before exploring further.

# ADK Streaming API

> Partial events, STREAM_DELTA artifacts, and file artifacts in the ADK plugin.

This page describes how ADK agents stream output to A2A clients through partial events and artifacts.

## 1. Partial Events — Real-time Text Streaming

Yield ADK events with `partial=True` to stream text chunks to the client in real time. Each chunk
is forwarded as a transitory `STREAM_DELTA` artifact update:

```python theme={null}
from google.adk.events import Event
from google.adk.agents import BaseAgent
from google.genai import types


class MyAgent(BaseAgent):
    async def _run_async_impl(self, ctx):
        # Stream text in chunks
        for chunk in ["Hello", " world", "!"]:
            yield Event(
                author=self.name,
                content=types.Content(
                    role="model",
                    parts=[types.Part(text=chunk)],
                ),
                partial=True,
            )

        # Final non-partial event closes the stream
        yield Event(
            author=self.name,
            content=types.Content(
                role="model",
                parts=[types.Part(text="Hello world!")],
            ),
            partial=False,
        )
```

The `STREAM_DELTA` artifact is **transitory** — it is not persisted to the
Task's durable state. Partial and non-partial ADK event content may populate
the SDK-managed response buffer for the current turn. If that buffer stays
empty, Aion falls back to `a2a_outbox` and then framework-native fallback
rules. See [Message Mapping](./message-mapping) for outbound precedence rules.

## 2. Non-partial Events

When a non-partial ADK event is yielded:

1. The open `STREAM_DELTA` stream is closed (if streaming was active).
2. Content parts are emitted as a `TaskStatusUpdateEvent(working, message=...)`.
3. Artifacts declared in `event.actions.artifact_delta` are loaded and forwarded as
   `TaskArtifactUpdateEvent`.

## 3. File and Data Artifacts

Use `ctx.artifact_service` to save file or data artifacts. Saved artifacts are automatically
forwarded to the client as `TaskArtifactUpdateEvent`:

```python theme={null}
from google.adk.agents import BaseAgent
from google.adk.events import Event, EventActions
from google.genai import types


class MyAgent(BaseAgent):
    async def _run_async_impl(self, ctx):
        pdf_bytes = b"..."  # your PDF content

        artifact = types.Part(
            inline_data=types.Blob(mime_type="application/pdf", data=pdf_bytes)
        )
        version = await ctx.artifact_service.save_artifact(
            app_name=ctx.app_name,
            user_id=ctx.user_id,
            session_id=ctx.session.id,
            filename="report.pdf",
            artifact=artifact,
        )

        # Declare the saved artifact in the event so it is forwarded to the client
        yield Event(
            author=self.name,
            actions=EventActions(artifact_delta={"report.pdf": version}),
        )
```

Each entry in `artifact_delta` maps a filename to its saved version. Aion Server automatically
forwards each declared artifact to the client as a `TaskArtifactUpdateEvent`.

## 4. Artifact Namespaces

The filename prefix controls artifact scope:

| Prefix     | Scope                                                  |
| ---------- | ------------------------------------------------------ |
| `user:...` | User-scoped — shared across all sessions for this user |
| *(none)*   | Session-scoped — private to the current context        |

Examples:

```python theme={null}
# Session-scoped artifact (default)
await ctx.artifact_service.save_artifact(..., filename="report.pdf", ...)

# User-scoped artifact (persists across sessions)
await ctx.artifact_service.save_artifact(..., filename="user:profile.json", ...)
```

For artifact storage backend configuration, see [Artifact Storage](./artifact-storage).

## Related Pages

* [Artifact Builders](/sdk/python/messaging/artifacts) — `url_artifact`, `file_artifact`, `data_artifact` reference
* [Card](/sdk/python/messaging/card) — Card builder API reference