Problem with graph.astream() with stream_mode="message"

[moonseyes]

I am having trouble with using .astream() with stream_mode="message" as follow:

async for chunk in graph.astream(
    {
        "question": question
    },
    stream_mode="messages"
):  
    print(chunk)

I want to be able to stream each token directly from llm any time it is invoked in any node, using .astream(). However, with the code above, the graph still run with no error, but no chunk is printed.
If I change from astream to stream and remove async, the chunks are printed as expected for messages mode.
If I keep astream and change stream_mode to values, updates, the chunks are printed as expected for values and updates modes.
However, I want to use both astream and messages mode together.
Does anyone run into this problem? Is there a fix to this?

[vbarda]

which python version are you using? this is likely due to using python < 3.11

[moonseyes]

I see. I am using python 3.10. I will try 3.11 to check. Thank you.

[zhoujz10]

I see. I am using python 3.10. I will try 3.11 to check. Thank you.

Hi, have you solved this issue by upgrading python? Because I'm using Python3.13 and I've got this problem too. thanks.

[moonseyes]

I see. I am using python 3.10. I will try 3.11 to check. Thank you.

Hi, have you solved this issue by upgrading python? Because I'm using Python3.13 and I've got this problem too. thanks.

Hello. Yes, I tried 3.11 and it works. I don't know about 3.13 though.

[Maanaesh]

You've been a lifesaver - I've been banging my head trying to figure out what went wrong with my staging and local setup!

[pedroslev]

its not just the py version but also langgraph sdk lib versions. I was using langgraph 0.2.x with py 3.11.9 and trying to stream output tokens. Tokens just did not come out and the system was idle.

I just wiped every langgraph/langchain/langsmith lib on the proyect and reinstalled with the latest, refactored some code to make it work and now streaming works perfectly with graph.stream method using stream_mode="messages".

Hope this info helps :)