What is the difference between OpenAI Assistants API and Chat Completions API

Chat Completions API: Basics and Use Cases

The Chat Completions API is our go-to for generating text completions based on input prompts. It’s built around the concept of Messages and uses specified Models (e.g., GPT-3.5-turbo, GPT-4) to perform completions.


  • Stateless: It doesn’t maintain conversation history or state.
  • Manual Management: Requires handling conversation state, tool definitions, and code execution on the developer’s end.

Ideal for:

  • Simple query-response interactions.
  • Applications where conversation context is either minimal or managed externally.

Assistants API: Enhanced Capabilities

The Assistants API represents an evolution, introducing statefulness and context-aware interactions. It’s built on three primary primitives:

  • Assistants: Include a base model plus instructions, tools, and context documents.
  • Threads: Maintain the state of a conversation, allowing for persistent context.
  • Runs: Facilitate the execution of an Assistant on a Thread, supporting textual responses and tool usage.


  • Thread and Memory Management: Server-side storage of message history and conversation state.
  • Sliding Window: Automatic context window management.
  • Tools Integration: Optional use of tools to enhance capabilities.
  • Knowledge Retrieval: Easy seeding with a knowledge base for efficient information retrieval.
  • Code Interpreter: Supports Python code execution for complex problem-solving.
  • Functions: Allows invocation of third-party tools and APIs.

Ideal for:

  • Complex conversational applications requiring persistent context.
  • Scenarios involving sophisticated interaction capabilities, like dynamic information retrieval or on-the-fly code execution.

Choosing Between the APIs

When deciding which API to use for a project, consider the following:

  • Statefulness: Do you need to maintain a conversation history?
  • Complexity: How complex are the interactions? Do they require context understanding over multiple exchanges?
  • Integration Needs: Will you need to integrate external tools or data sources?
  • Development Overhead: Are you equipped to manage the additional complexity that comes with stateful interactions?


Both the Chat Completions API and the Assistants API offer powerful capabilities for developing AI-driven applications. The choice between them should be guided by the specific needs of your project, considering factors like statefulness, interaction complexity, and integration requirements. By leveraging the strengths of each API, we can continue to push the boundaries of what’s possible with AI in our products and services.