Is streaming of new "custom" tool calls supported using Chat Completions?

[AmevinLS]

Context:

In the documentation here, an example is given for passing "custom" tools to models using the Chat Completions API.

However, in the chat completion chunk object described here, the choices.delta.tool_calls only seems to support type="function" with no mention of "custom". The same is reflected in the openai python SDK, currently leading to among other things typing issues in downstream custom code.

Question:

So does this mean that streaming from Chat Completions while passing "custom" tools isn't supported? Or perhaps is the API definition incomplete?

Thanks in advance.