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Task a with path ('__pregel_pull', 'a') wrote to unknown channel remaining_steps, ignoring it. #944

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opened 2026-02-20 17:42:28 -05:00 by yindo · 3 comments
yindo commented 2026-02-20 17:42:28 -05:00
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Originally created by @pi-crust on GitHub (Aug 27, 2025).

Checked other resources

  • This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
  • I added a clear and detailed title that summarizes the issue.
  • I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example).
  • I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue.

Example Code

import operator
from typing import Annotated, Literal
from typing_extensions import TypedDict
from langgraph.graph import StateGraph, START, END
from langgraph.managed.is_last_step import RemainingSteps


class State(TypedDict):
    aggregate: Annotated[list, operator.add]
    remaining_steps: RemainingSteps


def a(state: State):
    print(f'Node A sees {state["aggregate"]}')
    return State(aggregate=["A"], remaining_steps=10)


def b(state: State):
    print(f'Node B sees {state["aggregate"]}')
    return State(aggregate=["B"])


# Define nodes
builder = StateGraph(State)
builder.add_node(a)
builder.add_node(b)


# Define edges
def route(state: State) -> Literal["b", END]:
    if state["remaining_steps"] <= 2:
        return END
    else:
        return "b"


builder.add_edge(START, "a")
builder.add_conditional_edges("a", route)
builder.add_edge("b", "a")
graph = builder.compile()

# Test it out
result = graph.invoke({"aggregate": []}, {"recursion_limit": 4})
print(result)

Error Message and Stack Trace (if applicable)

Task a with path ('__pregel_pull', 'a') wrote to unknown channel remaining_steps, ignoring it.

Description

I understand that remaining_steps is automatically tracked, however when we pass the variable to the state, we get the following error
Task a with path ('__pregel_pull', 'a') wrote to unknown channel remaining_steps, ignoring it.

How could we fix this ?

System Info

Python Version: 3.12.0

name = "langgraph", version = "0.6.4"
name = "langgraph-api", version = "0.2.128"
name = "langgraph-sdk", version = "0.2.0"

Originally created by @pi-crust on GitHub (Aug 27, 2025). ### Checked other resources - [x] This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/). - [x] I added a clear and detailed title that summarizes the issue. - [x] I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example). - [x] I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue. ### Example Code ```python import operator from typing import Annotated, Literal from typing_extensions import TypedDict from langgraph.graph import StateGraph, START, END from langgraph.managed.is_last_step import RemainingSteps class State(TypedDict): aggregate: Annotated[list, operator.add] remaining_steps: RemainingSteps def a(state: State): print(f'Node A sees {state["aggregate"]}') return State(aggregate=["A"], remaining_steps=10) def b(state: State): print(f'Node B sees {state["aggregate"]}') return State(aggregate=["B"]) # Define nodes builder = StateGraph(State) builder.add_node(a) builder.add_node(b) # Define edges def route(state: State) -> Literal["b", END]: if state["remaining_steps"] <= 2: return END else: return "b" builder.add_edge(START, "a") builder.add_conditional_edges("a", route) builder.add_edge("b", "a") graph = builder.compile() # Test it out result = graph.invoke({"aggregate": []}, {"recursion_limit": 4}) print(result) ``` ### Error Message and Stack Trace (if applicable) ```shell Task a with path ('__pregel_pull', 'a') wrote to unknown channel remaining_steps, ignoring it. ``` ### Description I understand that remaining_steps is automatically tracked, however when we pass the variable to the state, we get the following error `Task a with path ('__pregel_pull', 'a') wrote to unknown channel remaining_steps, ignoring it.` How could we fix this ? ### System Info Python Version: 3.12.0 name = "langgraph", version = "0.6.4" name = "langgraph-api", version = "0.2.128" name = "langgraph-sdk", version = "0.2.0"
yindo added the bugpending labels 2026-02-20 17:42:28 -05:00
yindo closed this issue 2026-02-20 17:42:28 -05:00
yindo commented 2026-02-20 17:42:28 -05:00
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@sydney-runkle commented on GitHub (Sep 8, 2025):

Ah yes, ManagedValues are not meant to be updated by the developer, they're tracked fully under the hood. It's not expected that state updates from nodes have managed values.

You can however check the state["remaining_steps"] as seen in the example in order to design exit conditions of your choosing.

@sydney-runkle commented on GitHub (Sep 8, 2025): Ah yes, `ManagedValue`s are not meant to be updated by the developer, they're tracked fully under the hood. It's not expected that state updates from nodes have managed values. You can however check the `state["remaining_steps"]` as seen in the example in order to design exit conditions of your choosing.
yindo commented 2026-02-20 17:42:28 -05:00
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@pi-crust commented on GitHub (Sep 9, 2025):

@sydney-runkle

We’ve recently been seeing the following error from the last node (before end), even though we’re not sending remaining_steps:
Task <node> remaining_steps with path () wrote to unknown channel remaining_steps, ignoring it.

@pi-crust commented on GitHub (Sep 9, 2025): @sydney-runkle We’ve recently been seeing the following error from the last node (before __end__), even though we’re not sending remaining_steps: `Task <node> remaining_steps with path () wrote to unknown channel remaining_steps, ignoring it.`
yindo commented 2026-02-20 17:42:29 -05:00
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@EPSIL0N1 commented on GitHub (Dec 22, 2025):

Any solution for this?

@EPSIL0N1 commented on GitHub (Dec 22, 2025): Any solution for this?
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Reference: langchain-ai/langgraph#944
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