# What is the return type of StateGraph.compile()?

**URL:** <https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074>\
**Category:** OSS Product Help\
**Tags:** intro-to-langgraph\
**Created:** [March 4, 2026, 11:05pm UTC](https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074 "2026-03-04T23:05:22Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![meharaz733](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/meharaz733/32/2201_2.png) [@meharaz733](https://forum.langchain.com/u/meharaz733)\
**Post date:** [March 4, 2026, 11:05pm UTC](https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074/1 "2026-03-04T23:05:22Z")

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Hi everyone,

I’m using **LangGraph** and I have an async helper to initialize my agent with a checkpointer:

> Blockquote  
> async def get\_agent():  
> “”“Get initialized agent with checkpointer.”“”  
> checkpointer = await get\_checkpointer()  
> return agent\_graph.compile(checkpointer=checkpointer)

My questions are:

1. What is the exact return type of agent\_graph.compile(checkpointer=checkpointer)?
2. Since this function is async, should I annotate it as → CompiledWorkflow or something else?
3. Can this compiled workflow be safely stored in FastAPI app.state?

I want to make sure I’m handling type hints and state correctly in an async environment.

Any clarification or examples would be greatly appreciated.

---

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**Author:** ![pawel-twardziak](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/pawel-twardziak/32/960_2.png) [@pawel-twardziak](https://forum.langchain.com/u/pawel-twardziak)\
**Post date:** [March 4, 2026, 11:33pm UTC](https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074/2 "2026-03-04T23:33:25Z")

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hi @meharaz733

**1. The Return Type Is `CompiledStateGraph`**

`StateGraph.compile()` returns a `CompiledStateGraph` object. You can see this directly in the source code:

```python
# langgraph/graph/state.py

def compile(
    self,
    checkpointer: Checkpointer = None,
    *,
    cache: BaseCache | None = None,
    store: BaseStore | None = None,
    interrupt_before: All | list[str] | None = None,
    interrupt_after: All | list[str] | None = None,
    debug: bool = False,
    name: str | None = None,
) -> CompiledStateGraph[StateT, ContextT, InputT, OutputT]:

```

Source: [`langgraph/graph/state.py` (line 1036)](https://github.com/langchain-ai/langgraph/blob/main/libs/langgraph/langgraph/graph/state.py#L1036-L1047)

**Import Path**

```python
from langgraph.graph.state import CompiledStateGraph

```

**Class Hierarchy**

`CompiledStateGraph` inherits from `Pregel`, which itself implements `Runnable`:

```txt
CompiledStateGraph
  └── Pregel
        └── PregelProtocol
              └── Runnable (LangChain)

```

This means your compiled graph supports all standard `Runnable` methods: `invoke()`, `ainvoke()`, `stream()`, `astream()`, `batch()`, etc.

**2. Type Annotation for Your Async Function**

Since `compile()` itself is not async (it’s a synchronous method), you annotate the return type directly with `CompiledStateGraph`:

```python
from langgraph.graph.state import CompiledStateGraph

async def get_agent() -> CompiledStateGraph:
    """Get initialized agent with checkpointer."""
    checkpointer = await get_checkpointer()
    return agent_graph.compile(checkpointer=checkpointer)

```

Note: `CompiledStateGraph` is generic (`CompiledStateGraph[StateT, ContextT, InputT, OutputT]`), but for most practical use cases the simple `CompiledStateGraph` annotation is sufficient.

**3. Storing the Compiled Graph in FastAPI’s `app.state`**

Yes, you can store it in `app.state`. The compiled graph object is reusable and thread-safe for concurrent invocations. A common pattern is:

```python
from contextlib import asynccontextmanager
from fastapi import FastAPI
from langgraph.graph.state import CompiledStateGraph

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Initialize once at startup
    app.state.agent = await get_agent()
    yield

app = FastAPI(lifespan=lifespan)

@app.post("/chat")
async def chat(message: str):
    result = await app.state.agent.ainvoke({"messages": [("user", message)]})
    return result

```

- Use `ainvoke()`/`astream()` in async contexts (not `invoke()`/`stream()`), as these are the async-native methods.
- The checkpointer must also be async-compatible. If you’re using `AsyncPostgresSaver` or `AsyncSqliteSaver`, they work natively in async FastAPI. Avoid synchronous checkpointers like `MemorySaver` in async code - they block the event loop.
- One compiled graph instance can handle multiple concurrent requests - each call to `ainvoke()`/`astream()` operates on its own thread/state based on the `thread_id` in the config.

### References

- [LangGraph Source – `StateGraph.compile()`](https://github.com/langchain-ai/langgraph/blob/main/libs/langgraph/langgraph/graph/state.py)
- [LangGraph Docs – StateGraph](https://langchain-ai.github.io/langgraph/reference/graphs/#langgraph.graph.state.StateGraph.compile)
- [LangGraph Docs – CompiledStateGraph](https://langchain-ai.github.io/langgraph/reference/graphs/#langgraph.graph.state.CompiledStateGraph)

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<div class="post-metadata">

**Author:** ![meharaz733](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/meharaz733/32/2201_2.png) [@meharaz733](https://forum.langchain.com/u/meharaz733)\
**Post date:** [March 5, 2026, 10:51am UTC](https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074/3 "2026-03-05T10:51:50Z")

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@pawel-twardziak thank you so much dude.

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**Author:** ![system](https://yyz1.discourse-cdn.com/flex007/user_avatar/forum.langchain.com/system/32/1_2.png) [@system](https://forum.langchain.com/u/system)\
**Post date:** [March 5, 2026, 10:52pm UTC](https://forum.langchain.com/t/what-is-the-return-type-of-stategraph-compile/3074/4 "2026-03-05T22:52:42Z")

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