# Streaming — Python

## Quick Start

```python
with client.messages.stream(
    model="claude-opus-5",
    max_tokens=64000,
    messages=[{"role": "user", "content": "Write a story"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)
```

### Async

```python
async with async_client.messages.stream(
    model="claude-opus-5",
    max_tokens=64000,
    messages=[{"role": "user", "content": "Write a story"}]
) as stream:
    async for text in stream.text_stream:
        print(text, end="", flush=True)
```

### Low-level: `stream=True`

`messages.stream()` (above) is the recommended helper — it accumulates state and exposes `text_stream` / `get_final_message()`. If you only need the raw event iterator and want lower memory use, pass `stream=True` to `messages.create()` instead:

```python
for event in client.messages.create(
    model="claude-opus-5",
    max_tokens=64000,
    messages=[{"role": "user", "content": "Write a story"}],
    stream=True,
):
    print(event.type)
```

No final-message accumulation is done for you in this form.

---

## Handling Different Content Types

Claude may return text, thinking blocks, or tool use. Handle each appropriately:

> **Fable 5 / Claude Opus 5 / Opus 4.8 / Opus 4.7 / Opus 4.6:** Use `thinking: {type: "adaptive"}`. On Claude Opus 5 adaptive is also what you get by omitting `thinking` entirely. On older models, use `thinking: {type: "enabled", budget_tokens: N}` instead.

```python
with client.messages.stream(
    model="claude-opus-5",
    max_tokens=64000,
    thinking={"type": "adaptive", "display": "summarized"},  # display opt-in: default is omitted (empty thinking text) on Fable 5 / Mythos 5 / Claude Opus 5 / Opus 4.8 / 4.7
    messages=[{"role": "user", "content": "Analyze this problem"}]
) as stream:
    for event in stream:
        if event.type == "content_block_start":
            if event.content_block.type == "thinking":
                print("\n[Thinking...]")
            elif event.content_block.type == "text":
                print("\n[Response:]")

        elif event.type == "content_block_delta":
            if event.delta.type == "thinking_delta":
                print(event.delta.thinking, end="", flush=True)
            elif event.delta.type == "text_delta":
                print(event.delta.text, end="", flush=True)
```

---

## Streaming with Tool Use

The Python tool runner supports streaming: pass `stream=True` to `client.beta.messages.tool_runner(...)` and each iteration yields a stream you consume event-by-event, with `get_final_message()` for the accumulated message per turn (see `shared/tool-use-concepts.md` → Tool Runner vs Manual Loop). Use the manual-loop pattern below only when you're not using the tool runner and need per-token streaming with tools:

```python
with client.messages.stream(
    model="claude-opus-5",
    max_tokens=64000,
    tools=tools,
    messages=messages
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

    response = stream.get_final_message()
    # Continue with tool execution if response.stop_reason == "tool_use"
```

---

## Getting the Final Message

```python
with client.messages.stream(
    model="claude-opus-5",
    max_tokens=64000,
    messages=[{"role": "user", "content": "Hello"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

    # Get full message after streaming
    final_message = stream.get_final_message()
    print(f"\n\nTokens used: {final_message.usage.output_tokens}")
```

---

## Streaming with Progress Updates

```python
def stream_with_progress(client, **kwargs):
    """Stream a response with progress updates."""
    total_tokens = 0
    content_parts = []

    with client.messages.stream(**kwargs) as stream:
        for event in stream:
            if event.type == "content_block_delta":
                if event.delta.type == "text_delta":
                    text = event.delta.text
                    content_parts.append(text)
                    print(text, end="", flush=True)

            elif event.type == "message_delta":
                if event.usage and event.usage.output_tokens is not None:
                    total_tokens = event.usage.output_tokens

        final_message = stream.get_final_message()

    print(f"\n\n[Tokens used: {total_tokens}]")
    return "".join(content_parts)
```

---

## Error Handling in Streams

```python
try:
    with client.messages.stream(
        model="claude-opus-5",
        max_tokens=64000,
        messages=[{"role": "user", "content": "Write a story"}]
    ) as stream:
        for text in stream.text_stream:
            print(text, end="", flush=True)
except anthropic.APIConnectionError:
    print("\nConnection lost. Please retry.")
except anthropic.RateLimitError:
    print("\nRate limited. Please wait and retry.")
except anthropic.APIStatusError as e:
    print(f"\nAPI error: {e.status_code}")
```

---

## Stream Event Types

| Event Type            | Description                 | When it fires                     |
| --------------------- | --------------------------- | --------------------------------- |
| `message_start`       | Contains message metadata   | Once at the beginning             |
| `content_block_start` | New content block beginning | When a text/tool_use block starts |
| `content_block_delta` | Incremental content update  | For each token/chunk              |
| `content_block_stop`  | Content block complete      | When a block finishes             |
| `message_delta`       | Message-level updates       | Contains `stop_reason`, usage     |
| `message_stop`        | Message complete            | Once at the end                   |

## Best Practices

1. **Always flush output** — Use `flush=True` to show tokens immediately
2. **Handle partial responses** — If the stream is interrupted, you may have incomplete content
3. **Track token usage** — The `message_delta` event contains usage information
4. **Use timeouts** — Set appropriate timeouts for your application
5. **Default to streaming** — Use `.get_final_message()` to get the complete response even when streaming, giving you timeout protection without needing to handle individual events
6. **Large `max_tokens` without streaming raises `ValueError`** — The SDK refuses non-streaming requests it estimates will exceed ~10 minutes (idle connections drop). Pass `stream=True` / use `messages.stream()`, or explicitly override `timeout`, to suppress the guard.
