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JetBrains

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JetBrains/CodeRuns on a laptop

JetBrains ships Mellum 2.1, a reasoning MoE for code

The updated Mellum packs 12B total parameters but activates just 2.5B, pairing code specialization with a new thinking mode under Apache-2.0.

Sep 20, 2026
CodeReasoning
Mellum2.1-12B-A2.5B-Thinking