chore: import upstream snapshot with attribution
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<!--
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name: 'Data: Streaming reference — Python'
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description: Python streaming reference including sync/async streaming and handling different content types
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ccVersion: 2.1.203
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-->
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# Streaming — Python
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## Quick Start
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```python
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with client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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messages=[{"role": "user", "content": "Write a story"}]
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) as stream:
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for text in stream.text_stream:
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print(text, end="", flush=True)
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```
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### Async
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```python
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async with async_client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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messages=[{"role": "user", "content": "Write a story"}]
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) as stream:
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async for text in stream.text_stream:
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print(text, end="", flush=True)
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```
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### Low-level: `stream=True`
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`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:
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```python
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for event in client.messages.create(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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messages=[{"role": "user", "content": "Write a story"}],
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stream=True,
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):
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print(event.type)
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```
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No final-message accumulation is done for you in this form.
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---
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## Handling Different Content Types
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Claude may return text, thinking blocks, or tool use. Handle each appropriately:
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> **Fable 5 / Opus 4.8 / Opus 4.7 / Opus 4.6:** Use `thinking: {type: "adaptive"}`. On older models, use `thinking: {type: "enabled", budget_tokens: N}` instead.
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```python
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with client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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thinking={"type": "adaptive", "display": "summarized"}, # display opt-in: default is omitted (empty thinking text) on Fable 5 / Mythos 5 / Opus 4.8 / 4.7
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messages=[{"role": "user", "content": "Analyze this problem"}]
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) as stream:
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for event in stream:
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if event.type == "content_block_start":
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if event.content_block.type == "thinking":
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print("\n[Thinking...]")
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elif event.content_block.type == "text":
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print("\n[Response:]")
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elif event.type == "content_block_delta":
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if event.delta.type == "thinking_delta":
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print(event.delta.thinking, end="", flush=True)
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elif event.delta.type == "text_delta":
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print(event.delta.text, end="", flush=True)
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```
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---
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## Streaming with Tool Use
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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:
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```python
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with client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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tools=tools,
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messages=messages
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) as stream:
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for text in stream.text_stream:
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print(text, end="", flush=True)
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response = stream.get_final_message()
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# Continue with tool execution if response.stop_reason == "tool_use"
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```
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---
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## Getting the Final Message
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```python
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with client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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messages=[{"role": "user", "content": "Hello"}]
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) as stream:
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for text in stream.text_stream:
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print(text, end="", flush=True)
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# Get full message after streaming
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final_message = stream.get_final_message()
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print(f"\n\nTokens used: {final_message.usage.output_tokens}")
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```
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---
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## Streaming with Progress Updates
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```python
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def stream_with_progress(client, **kwargs):
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"""Stream a response with progress updates."""
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total_tokens = 0
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content_parts = []
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with client.messages.stream(**kwargs) as stream:
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for event in stream:
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if event.type == "content_block_delta":
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if event.delta.type == "text_delta":
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text = event.delta.text
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content_parts.append(text)
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print(text, end="", flush=True)
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elif event.type == "message_delta":
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if event.usage and event.usage.output_tokens is not None:
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total_tokens = event.usage.output_tokens
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final_message = stream.get_final_message()
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print(f"\n\n[Tokens used: {total_tokens}]")
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return "".join(content_parts)
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```
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---
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## Error Handling in Streams
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```python
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try:
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with client.messages.stream(
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model="{{OPUS_ID}}",
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max_tokens=64000,
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messages=[{"role": "user", "content": "Write a story"}]
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) as stream:
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for text in stream.text_stream:
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print(text, end="", flush=True)
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except anthropic.APIConnectionError:
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print("\nConnection lost. Please retry.")
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except anthropic.RateLimitError:
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print("\nRate limited. Please wait and retry.")
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except anthropic.APIStatusError as e:
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print(f"\nAPI error: {e.status_code}")
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```
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---
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## Stream Event Types
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| Event Type | Description | When it fires |
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| --------------------- | --------------------------- | --------------------------------- |
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| `message_start` | Contains message metadata | Once at the beginning |
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| `content_block_start` | New content block beginning | When a text/tool_use block starts |
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| `content_block_delta` | Incremental content update | For each token/chunk |
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| `content_block_stop` | Content block complete | When a block finishes |
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| `message_delta` | Message-level updates | Contains `stop_reason`, usage |
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| `message_stop` | Message complete | Once at the end |
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## Best Practices
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1. **Always flush output** — Use `flush=True` to show tokens immediately
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2. **Handle partial responses** — If the stream is interrupted, you may have incomplete content
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3. **Track token usage** — The `message_delta` event contains usage information
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4. **Use timeouts** — Set appropriate timeouts for your application
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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
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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.
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