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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).
append_trailing_user_message.py
"""
Aws 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.aws import Claude

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

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

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

1

Set up your virtual environment

uv venv --python 3.12
source .venv/bin/activate

uv venv --python 3.12
.venv\Scripts\activate
2

Install dependencies

uv pip install -U agno aioboto3 boto3
3

Export your API keys

export AWS_ACCESS_KEY_ID="your_aws_access_key_id_here"
export AWS_SECRET_ACCESS_KEY="your_aws_secret_access_key_here"

$Env:AWS_ACCESS_KEY_ID="your_aws_access_key_id_here"
$Env:AWS_SECRET_ACCESS_KEY="your_aws_secret_access_key_here"
4

Run the example

Save the code above as append_trailing_user_message.py, then run:
python append_trailing_user_message.py
Full source: cookbook/90_models/aws/claude/append_trailing_user_message.py