ReasoningContentBlock Class — langchain Architecture

Source Code

libs/core/langchain_core/messages/content.py lines 456–492

class ReasoningContentBlock(TypedDict):
    """Reasoning output from a LLM.

    !!! note "Factory function"

        `create_reasoning_block` may also be used as a factory to create a
        `ReasoningContentBlock`. Benefits include:

        * Automatic ID generation (when not provided)
        * Required arguments strictly validated at creation time
    """

    type: Literal["reasoning"]
    """Type of the content block. Used for discrimination."""

    id: NotRequired[str]
    """Unique identifier for this content block.

    Either:

    - Generated by the provider
    - Generated by LangChain upon creation (`UUID4` prefixed with `'lc_'`))
    """

    reasoning: NotRequired[str]
    """Reasoning text.

    Either the thought summary or the raw reasoning text itself.

    Often parsed from `<think>` tags in the model's response.
    """

    index: NotRequired[int | str]
    """Index of block in aggregate response. Used during streaming."""

    extras: NotRequired[dict[str, Any]]
    """Provider-specific metadata."""