Mellum-4b-base is JetBrains' first open-source large language model (LLM) optimized for code-related tasks.

The best alternative to OpenAI Codex is Mellum, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to OpenAI Codex and six of them are so hopefully you can find a suitable replacement. Other interesting alternatives to OpenAI Codex are Mistral Code, JetBrains Junie, JetBrains AI Assistant and Hostinger Horizons.
Mellum-4b-base is JetBrains' first open-source large language model (LLM) optimized for code-related tasks.

Lightning-fast completions, deep code understanding, and agentic software engineering—right where you work.




You think it, Junie helps make it happen – right in your IDE. Available on IntelliJ IDEA, PyCharm, WebStorm and .




With JetBrains AI, your favorite tools gain new abilities while you are empowered with more information at your fingertips.

AI-driven no-code platform to create full-stack web apps quickly, featuring instant one-click deployment, integrated hosting, domain tools, professional email, real-time editing, version control, and rapid live publishing with a streamlined three-step process.




ShaggAi is a local-first AI automation and autocomplete platform that turns natural language into real actions on your PC and adds Copilot-style “ghost text” to almost any editor.



