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JetBrains Mellum 2 Review
Mellum 2 is an open-weight 12B-parameter Mixture-of-Experts (MoE) language model with 2.5B active parameters per token, specialized in software engineering.
shipped Jun 2, 2026aifreemium
1Mellum 2 is an open-weight 12B-parameter Mixture-of-Experts (MoE) language model.
2It utilizes 2.5B active parameters per token, optimizing for inference efficiency.
3The model is specialized in software engineering tasks, including code generation and editing.
4JetBrains open-sourced Mellum 2 on June 1, 2026, under the Apache 2.0 license.
JetBrains Mellum 2 at a Glance
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overview
What is JetBrains Mellum 2?
JetBrains Mellum 2 is a specialized AI model developed by JetBrains that enables software engineers to perform code generation, editing, and multi-step reasoning. It is an open-weight 12B-parameter Mixture-of-Experts (MoE) language model with 2.5B active parameters per token, optimized for inference efficiency on commodity GPUs. Mellum 2 is positioned as a "focal model" intended for integration into larger AI systems rather than a standalone frontier model. It handles a wide array of software development tasks, including debugging, multi-step reasoning, tool use and function calling, agentic coding, and conversational programming assistance. Its design supports routing and orchestration within multi-model AI systems, low-latency Retrieval-Augmented Generation (RAG) pipelines, and deployment as sub-agents in complex workflows. The model's Apache 2.0 license facilitates self-hosting and local deployment, addressing privacy and data residency requirements.
quick facts
Quick Facts
| Attribute | Value |
|---|---|
| Developer | JetBrains |
| Business Model | Open Source (Apache 2.0) with Freemium product integrations |
| Pricing | Free (model weights) / Freemium (JetBrains AI Assistant) |
| Platforms | API |
| API Available | Yes |
| Integrations | JetBrains IDEs |
| URL | https://arxiv.org/abs/2605.31268?utm_source=tldrai |
| API Docs URL | https://huggingface.co/JetBrains/Mellum2-12B-A2.5B-Instruct#install-from-pip-and-serve-model |
features
Key Features of JetBrains Mellum 2
JetBrains Mellum 2 incorporates several technical features designed for specialized software engineering tasks and efficient deployment within AI systems. Its architecture and licensing model provide flexibility for developers and organizations.
- 1Open-weight model released under the Apache 2.0 license, allowing for commercial use and self-hosting.
- 212B-parameter Mixture-of-Experts (MoE) architecture for enhanced performance.
- 3Utilizes 2.5B active parameters per token, contributing to inference efficiency.
- 4Specialized in software engineering, covering a broad range of development tasks.
- 5Capabilities for code generation, assisting in writing new code segments.
- 6Functionality for code editing, supporting modifications and refinements of existing code.
- 7API available for integration into custom applications and workflows.
- 8Supports multi-step reasoning, tool use, and function calling for complex tasks.
- 9Optimized for inference efficiency on commodity GPUs, reducing operational costs.
- 10Includes six distinct checkpoints: Base, Base-Pretrain, Instruct, Instruct-SFT, Thinking, and Thinking-SFT.
use cases
Who Should Use JetBrains Mellum 2?
JetBrains Mellum 2 is designed for specific applications within the AI and software development ecosystems, catering to developers and organizations seeking specialized, efficient, and controllable language models.
- 1Developers and organizations building multi-model AI systems that require efficient routing and orchestration of tasks.
- 2Engineers implementing low-latency Retrieval-Augmented Generation (RAG) pipelines where quick context summarization is critical.
- 3AI system architects designing complex agent pipelines that benefit from specialized sub-agents handling repetitive or latency-sensitive steps.
- 4Organizations with stringent privacy and data residency requirements that necessitate private and local deployment of AI models.
- 5Software engineers seeking assistance with code generation, debugging, multi-step reasoning, and conversational programming within their development workflows.
pricing
JetBrains Mellum 2 Pricing & Plans
JetBrains Mellum 2 is an open-weight model released under the Apache 2.0 license, which means the model weights are freely available for research and commercial use without direct cost. This allows for self-hosting and fine-tuning without licensing fees. The "freemium" designation primarily refers to its integration within JetBrains' commercial products, such as the JetBrains AI Assistant in their Integrated Development Environments (IDEs). While the core model is free to deploy, access to it through JetBrains' proprietary tools may involve subscription tiers for the AI Assistant, which typically includes a free tier with basic functionalities and paid tiers for advanced features and higher usage limits. Specific pricing for the JetBrains AI Assistant is subject to JetBrains' product offerings and is separate from the open-source model itself.
- 1Mellum 2 Model Weights: Free (Apache 2.0 License)
- 2JetBrains AI Assistant Integration: Freemium (specific tiers and pricing vary by JetBrains product)
competitors
JetBrains Mellum 2 vs Competitors
JetBrains Mellum 2 is positioned as a "focal model" within larger AI systems, emphasizing efficiency, low latency, and specialization in software engineering rather than broad generative intelligence. This differentiates it from many general-purpose LLMs and even some specialized coding assistants.
1
Integrates deeply with GitHub and major IDEs, offering AI-powered code suggestions, chat, and agentic workflows.
Unlike Mellum 2's open-weight model, Copilot uses proprietary models (OpenAI, Claude, Microsoft) and has a more established ecosystem with GitHub. It offers a freemium model, with a free tier for basic completions and paid tiers for advanced features and higher usage.
2
Deeply integrated with AWS services, providing specialized code suggestions, security scans, and autonomous agents for AWS-centric development.
Similar to Mellum 2, it offers a freemium model for individuals. While Mellum 2 is a general software engineering model, CodeWhisperer/Q Developer is particularly optimized for AWS APIs and infrastructure.
3
Emphasizes privacy and control with options for on-premises, VPC, or air-gapped deployments, and the ability to train on private codebases.
Tabnine is a pioneer in AI code completion and offers a freemium model like Mellum 2. Its focus on enterprise-grade privacy and customization, including BYOL (Bring Your Own LLM) and training on private repos, differentiates it from Mellum 2's open-weight model.
4
Code Llama (Meta)↗
An open-weight large language model family specifically designed for code generation, completion, and discussion, built on Llama 2.
Code Llama is an open-weight model, similar to Mellum 2's open-weight nature, but it is a foundational model rather than a direct end-user tool with a freemium offering. It is free for research and commercial use (with some exceptions for very large companies), which differs from Mellum 2's freemium product offering.
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Frequently Asked Questions
+What is JetBrains Mellum 2?
JetBrains Mellum 2 is a specialized AI model developed by JetBrains that enables software engineers to perform code generation, editing, and multi-step reasoning. It is an open-weight 12B-parameter Mixture-of-Experts (MoE) language model with 2.5B active parameters per token, optimized for inference efficiency on commodity GPUs.
+Is JetBrains Mellum 2 free?
The JetBrains Mellum 2 model weights are free and open-source under the Apache 2.0 license, allowing for free deployment and use. However, its integration into JetBrains' proprietary products, such as the JetBrains AI Assistant, operates on a freemium model, which may include free tiers with basic features and paid tiers for advanced functionalities.
+What are the main features of JetBrains Mellum 2?
JetBrains Mellum 2 features an open-weight 12B-parameter Mixture-of-Experts (MoE) architecture with 2.5B active parameters per token, specialized in software engineering tasks like code generation and editing. It supports multi-step reasoning, tool use, and is optimized for inference efficiency on commodity GPUs, with an API available for integration.
+Who should use JetBrains Mellum 2?
JetBrains Mellum 2 is intended for developers and organizations building multi-model AI systems, engineers implementing low-latency RAG pipelines, AI system architects designing complex agent workflows, and organizations requiring private or local AI model deployment. It also assists software engineers with code generation, debugging, and conversational programming.
+How does JetBrains Mellum 2 compare to alternatives?
JetBrains Mellum 2 is an open-weight, specialized 'focal model' for software engineering, emphasizing efficiency and integration into larger AI systems. This contrasts with proprietary models like GitHub Copilot and Amazon Q Developer, which offer deep ecosystem integrations. Unlike foundational models such as Code Llama, Mellum 2 is designed for specific tasks within AI workflows, and it differs from privacy-focused tools like Tabnine by being an open-source model rather than a service with extensive enterprise deployment options.
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