AI-Driven System Design: What is Large Language Model (LLM)?

July 2, 2026

URI Endpoint for chat completion:

  • POST https://api.openai.com/v1/chat/completions

Headers:

Authorization: Bearer YOUR_API_KEY Content-Type: application/json

Request Structure:

{
  "model": "gpt-4",
  "messages": [
    {"role": "system", "content": "You are a helpful assistant."},
    {"role": "user", "content": "Hello, who won the world cup in 2018?"}
  ],
  "temperature": 0.7
}

Response Structure:

{
  "id": "chatcmpl-7vghhBnMywafj2w",
  "object": "chat.completion",
  "created": 1692987875,
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "France won the World Cup in 2018."
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 35,
    "completion_tokens": 7,
    "total_tokens": 42
  }
}