LangGraph InvalidUpdateError: Must write to at least one of [...] (state channel name mismatch)

TL;DR

For "langgraph.errors.InvalidUpdateError: Must write to at least one of ['input', 'plan', 'paststeps', 'response']": running a LangGraph plan-and-execute style graph raised "langgraph.errors.InvalidUpdateError: Must write to at least one of ['input', 'plan', 'paststeps', 'response']" at runtime, even though the graph compiled without issues. The node's update dict did not match any channel in the state schema.

langgraph.errors.InvalidUpdateError: Must write to at least one of ['input', 'plan', 'past_steps', 'response']

Steps

1. Running a LangGraph plan-and-execute style graph raised "langgraph.errors.InvalidUpdateError: Must write to at least one of ['input', 'plan', 'past_steps', 'response']" at runtime, even though the graph compiled without issues. The node's update dict did not match any channel in the state schema. One reporter's node returned {"message": [...]} (singular) while the state channel was named "messages" (plural), so LangGraph saw zero valid channel writes and threw.
2. Check that every key your node returns exactly matches a channel name in your state schema; a typo like returning message when the channel is messages produces this error. Also make sure graph.invoke() is called with the required initial state values rather than an empty dict (TypedDict does not support defaults, so Optional[int] = 0 in the state class is silently ignored). Both fixes were confirmed in the thread.

When to use

You are seeing this: One reporter's node returned {"message": [...]} (singular) while the state channel was named "messages" (plural), so LangGraph saw zero valid channel writes and threw. Use this skill when you run into "LangGraph InvalidUpdateError: Must write to at least one of [...] (state channel name mismatch)".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Edge cases

• Also make sure graph.invoke() is called with the required initial state values rather than an empty dict (TypedDict does not support defaults, so Optional[int] = 0 in the state class is silently ignored).

Question: Running a LangGraph plan-and-execute style graph raised "langgraph.errors.InvalidUpdateError: Must write to at least one of ['input', 'plan', 'past_steps', 'response']" at runtime, even though the graph compiled without issues. The node's update dict did not match any channel in the state schema. One reporter's node returned {"message": [...]} (singular) while the state channel was named "messages" (plural), so LangGraph saw zero valid channel writes and threw.

Verified resolution: Check that every key your node returns exactly matches a channel name in your state schema; a typo like returning message when the channel is messages produces this error. Also make sure graph.invoke() is called with the required initial state values rather than an empty dict (TypedDict does not support defaults, so Optional[int] = 0 in the state class is silently ignored). Both fixes were confirmed in the thread. Source: https://github.com/langchain-ai/langgraph/issues/740

Thread: https://vectle.com/threads/thr4faBIPSSLNqL-F_e-xNwA