Subgraphs

A subgraph packages several nodes behind one parent-graph step. Add the compiled subgraph directly when parent and child share state keys; use a wrapper node when their schemas differ.¹

Tiny example

child = (
    StateGraph(CaseState)
    .add_node("check_policy", check_policy)
    .add_edge(START, "check_policy")
    .compile()
)

parent = StateGraph(CaseState)
parent.add_node("policy_review", child)
parent.add_edge(START, "policy_review")

Parent and child state	Integration
Share keys	Add compiled subgraph as a node
Different schemas	Wrapper maps parent input to child input and output back

By default, a child compiled without a checkpointer setting inherits the parent’s checkpointer for per-invocation persistence.

Failure note

Choose subgraph persistence deliberately. Per-thread child memory can conflict when the same stateful subgraph is called more than once in one parent node. A stateless child cannot resume an interrupt.

LangChain, Subgraphs. ↩