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

# Anthropic Append Trailing User Message

> Claude 4.6+ does not support assistant message prefill.

Claude 4.6+ does not support assistant message prefill. Enable `append_trailing_user_message` to append a trailing user turn when the conversation ends with an assistant message (e.g. during reasoning).

```python append_trailing_user_message.py theme={null}
"""
Anthropic Append Trailing User Message
======================================

Claude 4.6+ does not support assistant message prefill. Enable
`append_trailing_user_message` to append a trailing user turn when the
conversation ends with an assistant message (e.g. during reasoning).

Use `trailing_user_message_content` to customise the appended text (defaults to "continue").

Note: Claude 4.6+ models auto-detect and enable this flag automatically.
"""

from agno.agent import Agent
from agno.models.anthropic import Claude

# ---------------------------------------------------------------------------
# Create Agent
# ---------------------------------------------------------------------------

agent = Agent(
    model=Claude(id="claude-sonnet-4-6", append_trailing_user_message=True),
    reasoning=True,
    markdown=True,
)

# With custom trailing content
agent_custom = Agent(
    model=Claude(
        id="claude-sonnet-4-6",
        append_trailing_user_message=True,
        trailing_user_message_content=".",
    ),
    reasoning=True,
    markdown=True,
)

# ---------------------------------------------------------------------------
# Run Agent
# ---------------------------------------------------------------------------
if __name__ == "__main__":
    agent.print_response("What is 15 + 27?")
    agent_custom.print_response("What is 15 + 27?")
```

## Run the Example

<Steps>
  <Snippet file="create-venv-step.mdx" />

  <Step title="Install dependencies">
    ```bash theme={null}
    uv pip install -U agno anthropic
    ```
  </Step>

  <Step title="Export your Anthropic API key">
    <CodeGroup>
      ```bash Mac/Linux theme={null}
      export ANTHROPIC_API_KEY="your_anthropic_api_key_here"
      ```

      ```bash Windows theme={null}
      $Env:ANTHROPIC_API_KEY="your_anthropic_api_key_here"
      ```
    </CodeGroup>
  </Step>

  <Step title="Run the example">
    Save the code above as `append_trailing_user_message.py`, then run:

    ```bash theme={null}
    python append_trailing_user_message.py
    ```
  </Step>
</Steps>

Full source: [cookbook/90\_models/anthropic/append\_trailing\_user\_message.py](https://github.com/agno-agi/agno/blob/main/cookbook/90_models/anthropic/append_trailing_user_message.py)