langchain-ai/langgraph · error · ImportError

Please install langchain (`pip install langchain`) to use '<

Error message

Please install langchain (`pip install langchain`) to use '<provider>:<model>' string syntax for `model` parameter.

What it means

Error "Please install langchain (`pip install langchain`) to use '<provider>:<model>' string syntax for `model` parameter." thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:575

        tool_node = tools
    else:
        llm_builtin_tools = [t for t in tools if isinstance(t, dict)]
        tool_node = ToolNode([t for t in tools if not isinstance(t, dict)])
        tool_classes = list(tool_node.tools_by_name.values())

    is_dynamic_model = not isinstance(model, (str, Runnable)) and callable(model)
    is_async_dynamic_model = is_dynamic_model and inspect.iscoroutinefunction(model)

    tool_calling_enabled = len(tool_classes) > 0

    if not is_dynamic_model:
        if isinstance(model, str):
            try:
                from langchain.chat_models import (  # type: ignore[import-not-found]
                    init_chat_model,
                )
            except ImportError:
                raise ImportError(
                    "Please install langchain (`pip install langchain`) to "
                    "use '<provider>:<model>' string syntax for `model` parameter."
                )

            model = cast(BaseChatModel, init_chat_model(model))

        if (
            _should_bind_tools(model, tool_classes, num_builtin=len(llm_builtin_tools))  # type: ignore[arg-type]
            and len(tool_classes + llm_builtin_tools) > 0
        ):
            model = cast(BaseChatModel, model).bind_tools(
                tool_classes + llm_builtin_tools  # type: ignore[operator]
            )

        static_model: Runnable | None = _get_prompt_runnable(prompt) | model  # type: ignore[operator]
    else:
        # For dynamic models, we'll create the runnable at runtime
        static_model = None

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:575 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/5f43c14732781835. Report an issue: GitHub.