BerriAI/litellm · error · ValueError

Invalid ARN format: {arn}

Error message

Invalid ARN format: {arn}

What it means

Error "Invalid ARN format: {arn}" thrown in BerriAI/litellm.

Source

Thrown at litellm/llms/bedrock/chat/agentcore/transformation.py:177

        returns: "arn:aws:bedrock-agentcore:us-west-2:888602223428:runtime/hosted_agent_r9jvp-3ySZuRHjLC"
        """
        parts: Final = model.split("/", 1)
        if len(parts) != 2 or parts[0] != "agentcore":
            raise ValueError(
                "Invalid model format. Expected format: 'model=bedrock/agentcore/arn:aws:bedrock-agentcore:region:account:runtime/runtime_id'"
            )
        return parts[1]

    def _extract_region_from_arn(self, arn: str) -> str:
        """
        Extract region from ARN
        arn:aws:bedrock-agentcore:us-west-2:888602223428:runtime/hosted_agent_r9jvp-3ySZuRHjLC
        returns: us-west-2
        """
        parts: Final = arn.split(":")
        if len(parts) >= 4:
            return parts[3]
        raise ValueError(f"Invalid ARN format: {arn}")

    def _get_runtime_session_id(self, optional_params: dict) -> str:
        """
        Get or generate runtime session ID (must be 33+ chars)
        """
        session_id: Final = optional_params.get("runtimeSessionId", None)
        if session_id:
            verbose_logger.debug("Using provided runtimeSessionId: %s", session_id)
            return session_id

        # Generate a session ID with 33+ characters
        generated_id: Final = f"litellm-session-{uuid.uuid4()}"
        verbose_logger.debug("Generated new session ID: %s", generated_id)
        return generated_id

    def _get_runtime_user_id(self, optional_params: dict) -> str | None:
        """
        Get runtime user ID if provided

View on GitHub (pinned to 6c2dcb801b)

Solutions

1. Pass a valid AgentCore ARN.

When it happens

Trigger: Thrown at litellm/llms/bedrock/chat/agentcore/transformation.py:177 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@6c2dcb801b (2026-08-15). Data as JSON: /api/errors/a7ad26f75d090589. Report an issue: GitHub.