stream_options.include_usage = true 在最后⼀个响应块中{
  "stream": true,
  "stream_options": {
    "include_usage": true
  },
  "messages": [{"role": "user", "content": "简短介绍一下大模型"}],
  "model": "gpt-4"
}{
  "id": "chatcmpl-123456",
  "object": "chat.completion.chunk",
  "choices": [...],
  "usage": {
    "prompt_tokens": 15,
    "completion_tokens": 120,
    "total_tokens": 135
  }
}