Missing Reasoning Chain in streamText Response

[ConardLi]

Description

I'm working with the following streamText function that uses a streaming text generation model:

async chatStream(messages, options) {
  const lastMessage = messages[messages.length - 1];
  const prompt = lastMessage.content;
  const model = this._getModel();
  const stream = streamText({
    model,
    messages: this._convertJson(messages),
    temperature: options.temperature || this.modelConfig.temperature,
    topP: options.top_p || this.modelConfig.top_p,
    maxTokens: options.max_tokens || this.modelConfig.max_tokens,
  });
  return stream.toTextStreamResponse();
}

Expected:
Response should include both reasoning steps and final answer (chain-of-thought).

Actual:
Only the final answer is returned.

Possible Issues:

1. Missing parameters in streamText to enable reasoning generation.
2. toTextStreamResponse() method filters out reasoning content.
3. _convertJson() modifies messages in a way that suppresses reasoning.

Ask:
What parameter/config change is needed to include the reasoning chain?

AI SDK Version

• "ai": "^4.3.4",
• "@ai-sdk/openai": "^1.3.9",

[remorses]

A text stream only contains text so there would be no way to distinguish reasoning from the actual response. You should use a different response type to be able to access the reasoning thoughts.

[lgrammel]

If you want to forward reasoning information you need to use a data stream or in ai sdk 5 a ui message stream.