---
title: "JetBrains releases Mellum2.1, open 12B coding-agent model"
url: https://www.parallelquant.com/posts/jetbrains-releases-mellum2-1-open-12b-coding-agent-model-97ed5d
source_name: "MarkTechPost"
source_url: https://www.marktechpost.com/2026/10/08/jetbrains-releases-mellum2-1-a-12b-moe-open-model-for-coding-agents/
published: 2026-10-08T16:17:35.000Z
topics: ["open source", "llms"]
publisher: "Parallel Quant"
---

# JetBrains releases Mellum2.1, open 12B coding-agent model

*2026-10-08 · Source: [MarkTechPost](https://www.marktechpost.com/2026/10/08/jetbrains-releases-mellum2-1-a-12b-moe-open-model-for-coding-agents/)*

JetBrains released Mellum2.1, an Apache 2.0 mixture-of-experts model with 12B total and 2.5B active parameters. Reinforcement learning in real repositories lifted its SWE-bench Verified score from 2.0 to 47.0.

**Why it matters:** A 2.5B-active model reaching 47 on SWE-bench Verified shows how far repository-level RL can push small models. That makes capable coding agents feasible on modest or local hardware, and gives teams an open alternative to frontier APIs.

**Topics:** open source, llms

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Read the original: https://www.marktechpost.com/2026/10/08/jetbrains-releases-mellum2-1-a-12b-moe-open-model-for-coding-agents/
Canonical: https://www.parallelquant.com/posts/jetbrains-releases-mellum2-1-open-12b-coding-agent-model-97ed5d
Published by Parallel Quant — https://www.parallelquant.com