langgraph-tutorial.ipynb: AttributeError: 'tuple' object has no attribute 'invoke' i need help

[xiongzhenglong]

Title:
AttributeError: 'tuple' object has no attribute 'invoke' when using OpenRouter with LangChain on Colab

Issue Description:
I encountered the following error when running my LangChain app in Google Colab:

AttributeError: 'tuple' object has no attribute 'invoke'
The only change I've made to the original code is replacing the LLM with an OpenRouter model:

llm = ChatOpenAI(
model="openai/gpt-4o-mini",
openai_api_base="https://openrouter.ai/api/v1",
temperature=0
)
The traceback points specifically to the invocation of the LLM:

classification = llm.invoke([message]).content.strip()
Full error traceback:

---

AttributeError Traceback (most recent call last)
in <cell line: 0>()
5
6 state_input = {"text": sample_text}
----> 7 result = app.invoke(state_input)
8
9 print("Classification:", result["classification"])

6 frames
in classification_node(state)
6 )
7 message = HumanMessage(content=prompt.format(text=state["text"]))
----> 8 classification = llm.invoke([message]).content.strip()
9 return {"classification": classification}
10

AttributeError: 'tuple' object has no attribute 'invoke'
Could anyone help identify why this is happening? Thanks!