Does BAML support atomic list‑item streaming? I’m streaming a function that returns a list of union items (e.g., tool calls and messages). What I want: each list element should only appear once it’s fully complete—no partial updates to that element after it first shows up. Example shape: ⁨`type OutputItem = ToolCall | Message`⁩ ⁨`function Run(...) -> OutputItem[]`⁩ In practice, I still see partial updates: an item appears with placeholder/empty fields and then updates later as more tokens arrive. I’ve tried using ⁨`@@stream.done`⁩ on the output classes and also wrapping the union in a dedicated class with ⁨`@@stream.done`⁩, but list elements still update. Is “atomic list item” streaming supported? If yes, what’s the correct way to achieve it?

Does (T @stream.done)[] not work here?

Not in every test so far 🙁

That’s def a bug. Let me try and repro and hopefully we can fix this in either this release or next!

With this code, it does stream, but I get updates where I shouldn't: ⁨``` class ToolCall { name string parameters string @stream.done } class ExampleMessage { role string content string @stream.done } type OutputItem = ToolCall | ExampleMessage function Run(input: string) -> (OutputItem @stream.done)[] { client "Default" prompt #" Process the following input and return a list of tool calls and messages. {{ input }} {{ ctx.output_format }} "# } ```⁩

Ok perfect. Thanks for the easy repro

Let me know if it was a bug or if I'm messing up 🙂 first time using streaming. This would also be an interesting case for the docs. It's not obvious that you should be able to do this with list items 🙂

this appears to work https://cdn.discordapp.com/attachments/1467029752606101660/1467187048451674215/Screenshot_2026-01-31_at_8.57.24_AM.png?ex=697f77eb&is=697e266b&hm=ef8eecc1c386d0d0065030956bdc148f52a8649046f29193a5b993ea6a40e2b1&

Weird, I'm on BAML 0.218.1 and trying this: ⁨⁨```class ToolCall { name string parameters string @@stream.done } class ExampleMessage { role string content string @@stream.done } type OutputItem = ToolCall | ExampleMessage function Run(input: string) -> (OutputItem @stream.done)[] { client "Default" prompt #" Process the following input and return a list of tool calls and messages. {{ input }} {{ ctx.output_format }} "# }

⁩⁩

And this Python code:
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from __future__ import annotations from conference_concierge.baml_client.sync_client import b def main() -> None: stream = b.stream.Run( input=""" call 3 tools: - get_weather - add_reminder - reply_to_user and tell the user "hello world" """.strip() ) for chunk in stream: print("--------") for item in chunk: print(item) print("-------- Done --------") done = stream.get_final_response() print(done) if __name__ == "__main__": main()

⁩⁩

And the result is:
⁨⁨

-------- name='get_weather' parameters=None -------- name='get_weather' parameters='{}' name='add_reminder' parameters=None -------- name='get_weather' parameters='{}' name='add_reminder' parameters='{}' name='reply_to_user' parameters=None -------- name='get_weather' parameters='{}' name='add_reminder' parameters='{}' name='reply_to_user' parameters='{}' role='assistant' content='hello world' -------- name='get_weather' parameters='{}' name='add_reminder' parameters='{}' name='reply_to_user' parameters='{}' role='assistant' content='hello world' -------- Done -------- [ToolCall(name='get_weather', parameters='{}'), ToolCall(name='add_reminder', parameters='{}'), ToolCall(name='reply_to_user', parameters='{}'), ExampleMessage(role='assistant', content='hello world')] ```⁩⁩

i wonder if the llm is giving you a ⁨`{}`⁩ as paramters, i think it might be! you might prefer: ⁨`parameters map`⁩ as clearly the model doesn't like a pure string as that type

The parameters thing as a string was just an example, my real code has depeer structures. But yes looking forward to the fix of the streaming! 💪