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  * [ Pydantic AI  ](https://ai.pydantic.dev/)
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    * pydantic_ai
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      * [ pydantic_ai.models.groq  ](https://ai.pydantic.dev/api/models/groq/)
      * [ pydantic_ai.models.huggingface  ](https://ai.pydantic.dev/api/models/huggingface/)
      * [ pydantic_ai.models.instrumented  ](https://ai.pydantic.dev/api/models/instrumented/)
      * [ pydantic_ai.models.mcp_sampling  ](https://ai.pydantic.dev/api/models/mcp-sampling/)
      * [ pydantic_ai.models.mistral  ](https://ai.pydantic.dev/api/models/mistral/)
      * [ pydantic_ai.models.openai  ](https://ai.pydantic.dev/api/models/openai/)
      * [ pydantic_ai.models.openrouter  ](https://ai.pydantic.dev/api/models/openrouter/)
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      * [ pydantic_ai.usage  ](https://ai.pydantic.dev/api/usage/)
    * pydantic_evals
      * [ pydantic_evals.dataset  ](https://ai.pydantic.dev/api/pydantic_evals/dataset/)
      * [ pydantic_evals.evaluators  ](https://ai.pydantic.dev/api/pydantic_evals/evaluators/)
      * [ pydantic_evals.reporting  ](https://ai.pydantic.dev/api/pydantic_evals/reporting/)
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      * [ pydantic_evals.generation  ](https://ai.pydantic.dev/api/pydantic_evals/generation/)
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      * [ pydantic_graph  ](https://ai.pydantic.dev/api/pydantic_graph/graph/)
      * [ pydantic_graph.nodes  ](https://ai.pydantic.dev/api/pydantic_graph/nodes/)
      * [ pydantic_graph.persistence  ](https://ai.pydantic.dev/api/pydantic_graph/persistence/)
      * [ pydantic_graph.mermaid  ](https://ai.pydantic.dev/api/pydantic_graph/mermaid/)
      * [ pydantic_graph.exceptions  ](https://ai.pydantic.dev/api/pydantic_graph/exceptions/)
      * Beta API
        * [ pydantic_graph.beta  ](https://ai.pydantic.dev/api/pydantic_graph/beta/)
        * [ pydantic_graph.beta.graph  ](https://ai.pydantic.dev/api/pydantic_graph/beta_graph/)
        * [ pydantic_graph.beta.graph_builder  ](https://ai.pydantic.dev/api/pydantic_graph/beta_graph_builder/)
        * [ pydantic_graph.beta.step  ](https://ai.pydantic.dev/api/pydantic_graph/beta_step/)
        * [ pydantic_graph.beta.join  ](https://ai.pydantic.dev/api/pydantic_graph/beta_join/)
        * [ pydantic_graph.beta.decision  ](https://ai.pydantic.dev/api/pydantic_graph/beta_decision/)
        * pydantic_graph.beta.node  [ pydantic_graph.beta.node  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/)
          * [ node  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node)
          * [ StateT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StateT)
          * [ OutputT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.OutputT)
          * [ InputT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.InputT)
          * [ StartNode  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StartNode)
            * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StartNode.id)
          * [ EndNode  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.EndNode)
            * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.EndNode.id)
          * [ Fork  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork)
            * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.id)
            * [ is_map  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.is_map)
            * [ downstream_join_id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.downstream_join_id)
    * fasta2a
      * [ fasta2a  ](https://ai.pydantic.dev/api/fasta2a/)
  * Project
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    * [ Version policy  ](https://ai.pydantic.dev/version-policy/)


  * [ node  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node)
  * [ StateT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StateT)
  * [ OutputT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.OutputT)
  * [ InputT  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.InputT)
  * [ StartNode  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StartNode)
    * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.StartNode.id)
  * [ EndNode  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.EndNode)
    * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.EndNode.id)
  * [ Fork  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork)
    * [ id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.id)
    * [ is_map  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.is_map)
    * [ downstream_join_id  ](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.Fork.downstream_join_id)


  1. [ Pydantic AI  ](https://ai.pydantic.dev/)
  2. [ API Reference  ](https://ai.pydantic.dev/api/ag_ui/)
  3. [ pydantic_graph  ](https://ai.pydantic.dev/api/pydantic_graph/graph/)
  4. [ Beta API  ](https://ai.pydantic.dev/api/pydantic_graph/beta/)


# `pydantic_graph.beta.node`
Core node types for graph construction and execution.
This module defines the fundamental node types used to build execution graphs, including start/end nodes and fork nodes for parallel execution.
###  StateT `module-attribute`
```
StateT = TypeVar('StateT', infer_variance=True)

```

Type variable for graph state.
###  OutputT `module-attribute`
```
OutputT = TypeVar('OutputT', infer_variance=True)

```

Type variable for node output data.
###  InputT `module-attribute`
```
InputT = TypeVar('InputT', infer_variance=True)

```

Type variable for node input data.
###  StartNode
Bases: `Generic[](https://docs.python.org/3/library/typing.html#typing.Generic "typing.Generic")[OutputT[](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.OutputT "OutputT



      module-attribute
   \(pydantic_graph.beta.node.OutputT\)")]`
Entry point node for graph execution.
The StartNode represents the beginning of a graph execution flow.
Source code in `pydantic_graph/pydantic_graph/beta/node.py`
```
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```
| ```
class StartNode(Generic[OutputT]):
    """Entry point node for graph execution.

    The StartNode represents the beginning of a graph execution flow.
    """

    id = NodeID('__start__')
    """Fixed identifier for the start node."""

```

---|---
####  id `class-attribute` `instance-attribute`
```
id = NodeID('__start__')

```

Fixed identifier for the start node.
###  EndNode
Bases: `Generic[](https://docs.python.org/3/library/typing.html#typing.Generic "typing.Generic")[InputT[](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.InputT "InputT



      module-attribute
   \(pydantic_graph.beta.node.InputT\)")]`
Terminal node representing the completion of graph execution.
The EndNode marks the successful completion of a graph execution flow and can collect the final output data.
Source code in `pydantic_graph/pydantic_graph/beta/node.py`
```
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```
| ```
class EndNode(Generic[InputT]):
    """Terminal node representing the completion of graph execution.

    The EndNode marks the successful completion of a graph execution flow
    and can collect the final output data.
    """

    id = NodeID('__end__')
    """Fixed identifier for the end node."""

    def _force_variance(self, inputs: InputT) -> None:  # pragma: no cover
        """Force type variance for proper generic typing.

        This method exists solely for type checking purposes and should never be called.

        Args:
            inputs: Input data of type InputT.

        Raises:
            RuntimeError: Always, as this method should never be executed.
        """
        raise RuntimeError('This method should never be called, it is just defined for typing purposes.')

```

---|---
####  id `class-attribute` `instance-attribute`
```
id = NodeID('__end__')

```

Fixed identifier for the end node.
###  Fork `dataclass`
Bases: `Generic[](https://docs.python.org/3/library/typing.html#typing.Generic "typing.Generic")[InputT[](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.InputT "InputT



      module-attribute
   \(pydantic_graph.beta.node.InputT\)"), OutputT[](https://ai.pydantic.dev/api/pydantic_graph/beta_node/#pydantic_graph.beta.node.OutputT "OutputT



      module-attribute
   \(pydantic_graph.beta.node.OutputT\)")]`
Fork node that creates parallel execution branches.
A Fork node splits the execution flow into multiple parallel branches, enabling concurrent execution of downstream nodes. It can either map a sequence across multiple branches or duplicate data to each branch.
Source code in `pydantic_graph/pydantic_graph/beta/node.py`
```
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```
| ```
@dataclass
class Fork(Generic[InputT, OutputT]):
    """Fork node that creates parallel execution branches.

    A Fork node splits the execution flow into multiple parallel branches,
    enabling concurrent execution of downstream nodes. It can either map
    a sequence across multiple branches or duplicate data to each branch.
    """

    id: ForkID
    """Unique identifier for this fork node."""

    is_map: bool
    """Determines fork behavior.

    If True, InputT must be Sequence[OutputT] and each element is sent to a separate branch.
    If False, InputT must be OutputT and the same data is sent to all branches.
    """
    downstream_join_id: JoinID | None
    """Optional identifier of a downstream join node that should be jumped to if mapping an empty iterable."""

    def _force_variance(self, inputs: InputT) -> OutputT:  # pragma: no cover
        """Force type variance for proper generic typing.

        This method exists solely for type checking purposes and should never be called.

        Args:
            inputs: Input data to be forked.

        Returns:
            Output data type (never actually returned).

        Raises:
            RuntimeError: Always, as this method should never be executed.
        """
        raise RuntimeError('This method should never be called, it is just defined for typing purposes.')

```

---|---
####  id `instance-attribute`
```
id: ForkID

```

Unique identifier for this fork node.
####  is_map `instance-attribute`
```
is_map: bool[](https://docs.python.org/3/library/functions.html#bool)

```

Determines fork behavior.
If True, InputT must be Sequence[OutputT] and each element is sent to a separate branch. If False, InputT must be OutputT and the same data is sent to all branches.
####  downstream_join_id `instance-attribute`
```
downstream_join_id: JoinID | None

```

Optional identifier of a downstream join node that should be jumped to if mapping an empty iterable.
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