Caspar BroekhuizenandGitHub affaa90d2a fix(langgraph): fix graph rendering for defer=True (#6130)
### Description

Some graphs with `defer=True` nodes rendered incorrectly. E.g.:
* edge C2 -> E1 is missing and edge C2 -> END should not appear in #5772
* edge E3 -> END is missing and edge E -> END should not appear in #5182
* extra edge #5369

Fix:
* Record the destinations declared by get_static_writes for each node.
Build step_sources as a union of the runtime writes and the static
writes (instead of just runtime writes).
* Label deferred nodes with 'deferred'

### https://github.com/langchain-ai/langgraph/issues/5772

'Before' is how they were rendered before this PR

| No defer    | Before (defer `E1`) | After (defer `E1`)
| -------- | ------- | ------- |
| <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/0a9fc992-1b6a-4c6d-8752-de54c703c329"
/> | <img height="400" alt="defer_before"
src="https://github.com/user-attachments/assets/825b09fc-3fb8-461a-9928-20c8d9cfc533"
/> | <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/ce5334f7-b469-47b0-8f1e-35bda2544a4e"
/> |

Before:
* For deferred joins (NamedBarrierValueAfterFinish), a writer from an
upstream node may not produce a runtime task.writes entry until the
barrier opens. draw_graph() builds edges from task.writes, so one side
of the join (here C2) never gets recorded as a source, and C2 is seen as
a sink, so there is an implicit edge: C2 -> END edge added.

After:
* C2's write to the join channel is recorded even if the barrier hasn’t
opened. When E1 finally schedules, we correctly find both sources B2 and
C2 for the same trigger and emit edges: B2 -> E1 and C2 -> E1.

With C2 -> E1 present, C2 is no longer a terminus, so the unexpected
edge: C2 -> END is not added.

### Other graphs

Graphs for the most part remain unchanged. See: 

### #5182 

| No defer    | Before (defer `d`) | After (defer `d`)
| -------- | ------- | ------- |
| <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/3509d25c-f3ad-473c-b877-c155b8008cd5"
/> | <img height="400" alt="defer_before"
src="https://github.com/user-attachments/assets/7af38e77-eb70-414d-b8fe-667da943f9e0"
/> | <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/bc87a19f-b4fb-42d3-a6ee-5b0982d9af71"
/> |

### https://github.com/langchain-ai/langgraph/issues/5369

| No defer | Before (defer `595577`, `52642`) | After (defer `595577`,
`52642`)
| -------- | ------- | ------- |
| <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/7c0824ce-3921-4dce-bc16-278f64289d28"
/> | <img height="400" alt="defer_before"
src="https://github.com/user-attachments/assets/28661079-7502-4912-874b-c086c0204a87"
/> | <img height="400" alt="defer_after"
src="https://github.com/user-attachments/assets/2a04956a-ed79-40e5-98b8-f6ecb2597a2e"
/> |
2025-09-23 12:47:50 -07:00
2025-06-10 10:06:08 -07:00
2025-09-09 14:22:19 +00:00
2024-03-15 14:31:59 -07:00

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Trusted by companies shaping the future of agents including Klarna, Replit, Elastic, and more LangGraph is a low-level orchestration framework for building, managing, and deploying long-running, stateful agents.

Get started

Install LangGraph:

pip install -U langgraph

Then, create an agent using prebuilt components:

# pip install -qU "langchain[anthropic]" to call the model

from langgraph.prebuilt import create_react_agent

def get_weather(city: str) -> str:
    """Get weather for a given city."""
    return f"It's always sunny in {city}!"

agent = create_react_agent(
    model="anthropic:claude-3-7-sonnet-latest",
    tools=[get_weather],
    prompt="You are a helpful assistant"
)

# Run the agent
agent.invoke(
    {"messages": [{"role": "user", "content": "what is the weather in sf"}]}
)

For more information, see the Quickstart. Or, to learn how to build an agent workflow with a customizable architecture, long-term memory, and other complex task handling, see the LangGraph basics tutorials.

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LangGraph provides low-level supporting infrastructure for any long-running, stateful workflow or agent. LangGraph does not abstract prompts or architecture, and provides the following central benefits:

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LangGraphs ecosystem

While LangGraph can be used standalone, it also integrates seamlessly with any LangChain product, giving developers a full suite of tools for building agents. To improve your LLM application development, pair LangGraph with:

  • LangSmith — Helpful for agent evals and observability. Debug poor-performing LLM app runs, evaluate agent trajectories, gain visibility in production, and improve performance over time.
  • LangGraph Platform — Deploy and scale agents effortlessly with a purpose-built deployment platform for long running, stateful workflows. Discover, reuse, configure, and share agents across teams — and iterate quickly with visual prototyping in LangGraph Studio.
  • LangChain Provides integrations and composable components to streamline LLM application development.

Note

Looking for the JS version of LangGraph? See the JS repo and the JS docs.

Additional resources

  • Guides: Quick, actionable code snippets for topics such as streaming, adding memory & persistence, and design patterns (e.g. branching, subgraphs, etc.).
  • Reference: Detailed reference on core classes, methods, how to use the graph and checkpointing APIs, and higher-level prebuilt components.
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Acknowledgements

LangGraph is inspired by Pregel and Apache Beam. The public interface draws inspiration from NetworkX. LangGraph is built by LangChain Inc, the creators of LangChain, but can be used without LangChain.

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