JetBrains releases Mellum, an open-source AI coding model
JetBrains, the renowned software company behind popular development tools like IntelliJ IDEA and PyCharm, has officially released its first open AI model for code generation. The model, named Mellum, is now available on Hugging Face under the Apache 2.0 license — a move signaling JetBrains’ deeper commitment to accessible and focused AI tooling for developers.
A Purpose-Built Model for Code Completion
Mellum was originally launched in 2023 as an internal model powering JetBrains’ development suites. Now, the company has taken the next step by open-sourcing the model for broader use and experimentation. With 4 billion parameters and trained on over 4 trillion tokens — the equivalent of more than 120 billion lines of code — Mellum is engineered for code completion, assisting developers by predicting and suggesting the next piece of code based on the context provided.
JetBrains emphasizes that Mellum isn’t designed to be a catch-all model. Instead, it's purpose-built for high-precision applications within development environments, making it suitable for tasks like intelligent code suggestions, code understanding research, AI assistants, and educational tools.
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Training Mellum was no small feat. JetBrains leveraged a cluster of 256 Nvidia H200 GPUs over 20 days to bring the model to life. The training data included permissively licensed code from GitHub and supplementary text sources like English-language Wikipedia, carefully curated to ensure a clean and reliable base.
Fine-Tuning Required
Despite its powerful base, Mellum isn't plug-and-play. Developers must fine-tune the model before use. JetBrains has released a few pre-fine-tuned versions for Python, but these are intended for evaluation and research rather than production deployment.
The company warns that like any AI model trained on public code, Mellum may inherit biases and could generate code that isn't secure or vulnerability-free. A 2023 Synk survey revealed that more than half of organizations face security issues with AI-generated code — a challenge Mellum users will need to keep in mind.
A Step Toward Focused AI Development
In its blog post, JetBrains made it clear that Mellum isn’t about competing with massive general-purpose models. Instead, it’s about focus and refinement, designed to evolve through community collaboration and targeted experimentation.
“This is just the beginning,” JetBrains wrote. “We’re not chasing generality — we’re building focus. If Mellum sparks even one meaningful experiment, contribution, or collaboration, we would consider it a win.”
With the release of Mellum, JetBrains is entering the AI coding landscape not with hype, but with a well-aimed offering that complements its developer-centric ecosystem. As the community begins to explore what Mellum can do, the impact of open, focused AI models on the future of programming is just beginning to unfold.
