AWS Append Trailing User Message

Append trailing user messages when Claude 4.6+ ends with an assistant response.

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).

The source configures both variants but sends fresh user-only prompts, so no trailing turn is needed. Use the assistant-ending conversation in the run step to exercise the behavior.

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

Set up your virtual environment

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

Install dependencies

uv pip install -U agno "anthropic[bedrock]" aioboto3 boto3

Configure AWS access

Select a source region that supports the model or inference profile in the example. A geographic profile such as us. routes across the source and destination regions listed for that profile; a global. profile can route globally. Verify the model's regional availability and your IAM permission to invoke it. For Anthropic models, complete the account's first-use model access requirements.

export AWS_REGION="us-east-1"
export AWS_ACCESS_KEY_ID="your_aws_access_key_id"
export AWS_SECRET_ACCESS_KEY="your_aws_secret_access_key"
# Required when using temporary credentials:
# export AWS_SESSION_TOKEN="your_aws_session_token"

Use credentials and any session token from the same session. Change AWS_REGION if you choose another supported source region. These examples use AWS credentials; agno.models.aws.Claude does not accept an Anthropic API key or a Bedrock API key in place of them.

Run the example

Save the code above as append_trailing_user_message.py. Replace both print_response calls under the main guard with:

from agno.models.message import Message

for configured_agent in (agent, agent_custom):
    configured_agent.print_response([
        Message(role="user", content="What is 15 + 27?"),
        Message(role="assistant", content="15 + 27 = 42."),
    ])

The outgoing requests append continue and . respectively. Then run:

python append_trailing_user_message.py

Full source: cookbook/90_models/aws/claude/append_trailing_user_message.py