[Bug] Stream doesn't work with Deep Research model

[kenshin54]

🐛 Describe the Bug

We tested the streaming API with different models with same code, the first token received with Deep Research model is almost same as the non-streaming version.

✅ Expected Behavior

The tokens should be streamed with Deep Research model.

❌ Actual Behavior

The time used between stream vs no stream are almost same.

🔄 Steps to Reproduce

import OpenAI from 'openai';

async function noStream(model: string) {
  const client = new OpenAI({
    apiKey: process.env['PERPLEXITY_API_KEY'],
    baseURL: 'https://api.perplexity.ai',
  });

  const t1 = new Date().getTime();

  await client.chat.completions.create({
    messages: [
      {
        role: 'system',
        content: 'Be precise and concise.',
      },
      {
        role: 'user',
        content: 'How many stars are there in our galaxy?',
      },
    ],
    model,
    stream: false,
  });

  const t2 = new Date().getTime();
  console.log(`Model: ${model}, response time: ${t2 - t1}ms`);
}

async function stream(model: string) {
  const client = new OpenAI({
    apiKey: process.env['PERPLEXITY_API_KEY'],
    baseURL: 'https://api.perplexity.ai',
  });

  const t1 = new Date().getTime();

  const stream = await client.chat.completions.create({
    messages: [
      {
        role: 'system',
        content: 'Be precise and concise.',
      },
      {
        role: 'user',
        content: 'How many stars are there in our galaxy?',
      },
    ],
    model,
    stream: true,
  });

  for await (const _chunk of stream) {
    const t2 = new Date().getTime();
    console.log(`Model: ${model}, first token received in: ${t2 - t1}ms`);
    break;
  }
}

const models = [
  'sonar',
  'sonar-pro',
  'sonar-reasoning',
  'sonar-reasoning-pro',
  'sonar-deep-research',
];

console.log('No stream:');
for (const model of models) {
  await noStream(model);
}

console.log('Stream:');
for (const model of models) {
  await stream(model);
}

📌 API Request & Response (if applicable)

🌍 Environment

• API Version: sonar-deep-research
• SDK (if applicable): I used OpenAI node client for chat completions API, but it should be same with raw HTTP call.
• Operating System: MacOS
• Authentication Type: API Key

📎 Logs or Screenshots (if applicable)