What Large Language Model Does GitHub Copilot Use?

If you use GitHub Copilot regularly, you’ve probably wondered what’s actually powering it. When it finishes your function before you do, it feels like magic. When Copilot Chat explains a complex class hierarchy in clean, structured language, it feels like you’re talking to a senior engineer. And when it occasionally produces something that almost works but not quite, you’re reminded that there’s a probabilistic engine underneath the surface. So what large language model does GitHub Copilot use? The honest answer is this: Copilot started with OpenAI Codex , a GPT-3–based model optimized for code, and has since evolved into a multi-model system that incorporates GPT-4–class models for advanced reasoning features. It does not run on one single static model. It uses different large language models depending on what you’re asking it to do. If you want to understand Copilot properly, you need to understand that layered architecture. Let’s break it down clearly and in depth. What an LLM actua