Mellum 2 Models by JetBrains
JetBrains releases · 2 in the last 12 monthsChangelog →
2 models2026Up to 128K ctx
Last refreshed 2026-10-08. Next refresh: weekly.
Details
ResearcherJetBrains
LicenseApache 2.0OSI-approved
Commercial useCommercial use: permitted
Models2
Released2026
Max context128K
Capabilities
ReasoningAll models
JSON / Tool useAll models
About
Mellum 2 is JetBrains' 12B mixture-of-experts open model family for software engineering (2.5B active parameters per token, 131K context). Mellum2 (2026-06) and Mellum2.1 Thinking (2026-10-08) share the architecture; 2.1 is a post-training/RL upgrade for agentic coding.
Decision facts
- Best fit
- codereasoningJSON / Tool use
- Capability starting point
- Mellum2.1 Thinking with 128K context and reasoning and JSON / Tool use
- Lowest tracked input
- Not tracked
- Closest related family
- Mellum
Current Variants
Use-when guidance is based on each model's tracked capabilities, context window, release date, and replacement status.
2 in view
Mellum2.1 ThinkingCurrent
Use when the workload needs code, 128K context, and reasoning.
2026-10code128K contextreasoning
Mellum2 12BCurrent
Use when the workload needs code, 128K context, and reasoning.
2026-06code128K contextreasoning
| Model | Use when | Released | Signals | Status |
|---|---|---|---|---|
| Mellum2.1 Thinking | Use when the workload needs code, 128K context, and reasoning. | 2026-10 | code128K contextreasoning | Current |
| Mellum2 12B | Use when the workload needs code, 128K context, and reasoning. | 2026-06 | code128K contextreasoning | Current |
Release Timeline
2 release groups2026-10
1 current
Mellum2.1 Thinking
Currentcode128K contextreasoning
2026-06
1 current
Mellum2 12B
Currentcode128K contextreasoning
Specifications(2 models)
| Model | Released | Context | Parameters | Reasoning | JSON / Tool use |
|---|---|---|---|---|---|
| Mellum2.1 Thinking | 2026-10 | 128K | 12B (2.5B active) | Yes | Yes |
| Mellum2 12B | 2026-06 | 128K | 12B (2.5B active) | Yes | Yes |