Mastering Generative AI with OpenAI
Building an Interactive Chatbot
Word Completion vs Chat Completion
Before integrating a chatbot into your application, it’s essential to understand the difference between word completion and chat completion. Although both use the same underlying GPT-3.5-Turbo model, their usage patterns—and the way they manage context—are very different.
What Is Word Completion?
Word completion is a stateless API call. You send a single prompt, and the model returns a continuation without retaining any memory of previous interactions.
Key characteristics:
- Single-shot responses
- No conversation history
- Simpler, lower token usage
What Is Chat Completion?
Chat completion is stateful. You maintain a record of all messages in a messages
array, allowing the model to build on past user and assistant exchanges.
How Chat Completion Works
- You create an ordered
messages
list. - Each entry has a
role
: system, user, or assistant. - You submit the full history each time you call the API.
- The model returns a response that accounts for all previous context.
Roles in the messages
Array
Role | Description | Example |
---|---|---|
system | Sets global instructions or persona | “You are a physics professor.” |
user | Represents the human’s input at each turn | “Explain quantum mechanics in simple terms.” |
assistant | Model-generated responses that continue the conversation context | “Quantum mechanics is the study of matter at very small scales…” |
When to Use Each API
- Use word completion for simple text continuations, code generation, or single-turn tasks.
- Use chat completion for multi-turn conversations, contextual assistants, and applications that require stateful interaction.
Sample Chat Completion Request
POST https://api.openai.com/v1/chat/completions
Content-Type: application/json
Authorization: Bearer YOUR_API_KEY
{
"model": "gpt-3.5-turbo",
"messages": [
{ "role": "system", "content": "You are a helpful assistant." },
{ "role": "user", "content": "Explain photosynthesis." }
]
}
Comparison at a Glance
Feature | Word Completion | Chat Completion |
---|---|---|
Context Handling | Stateless | Stateful via messages array |
Best for | Single-turn prompts | Multi-turn conversations |
Token Efficiency | Fewer overhead tokens | More overhead tokens for history |
Recommended Model | GPT-3.5-Turbo | GPT-3.5-Turbo |
Further Reading and References
- OpenAI Chat Completion API Reference
- OpenAI Completion API Reference
- Kubernetes Basics
- Terraform Registry
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