In this blog, we are going to explore some key differences between chat completion models (like those provided via the Chat Completions endpoint) and the more advanced OpenAI Assistance API. We will break down how these two approaches handle messages, conversation history, large documents, coding tasks, context window limits, and more. We will also look at how the Assistance API provides additional tools — such as code interpreters, document retrieval, and function calling — that overcome many limitations of chat completions.

Understanding Chat Completion Models

Chat completion models, such as GPT‑4 or GPT‑4o, typically expect a sequence of messages as input. The usual process is simple:

You send a list of messages to the model.
The model generates a response.
You receive the response as output.

Example Flow of Chat Completions

You ask: “What’s the capital of Japan?”