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Mellum2.1

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JetBrains' open 12B mixture-of-experts coding model with 2.5B parameters active per token under Apache 2.0

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About Mellum2.1

Mellum2.1 updates JetBrains' Mellum2 coding model. It is published with open weights, licensed under Apache 2.0. The model uses a mixture-of-experts layout: 12 billion parameters in total, 2.5 billion active, and JetBrains dates its release to around 8 October 2026.

What Mellum2.1 does

  • Agentic coding: works inside a repository, runs commands and calls tools.
  • Coding and reasoning: tackles hard coding, maths and reasoning problems without an agent setup.
  • Speed: JetBrains says multi-token prediction makes one request roughly 1.6 times quicker.
  • Throughput: on one H200 GPU under heavy load, serves almost twice as many tokens as Qwen3.5-9B, per JetBrains' announcement.

Who it works with

Its open weights under Apache 2.0 allow teams to host the model themselves.

Key facts

  • Developer: JetBrains
  • Context window: 131,072 tokens, per the model card
  • Licence: Apache 2.0

Profile written by TrustList from the business's own published information, Oct 2026.

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Trust Score

4/ 100
Trust Score: New

An earned signal from verification, reviews, awards, transparency and engagement - the vendor can't buy it.

Verification
0/100 · 20%
Reviews
0/100 · 30%
Awards
0/100 · 15%
Transparency
18/100 · 20%
Engagement
0/100 · 15%
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Updated 10/9/2026

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