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JETBRAINS · FIELD VERIFIED

Mellum2.1-12B-A2.5B-Thinking

Primary sources last checked on 11 Oct 2026. Verification freshness is tracked separately from factual change, and unknown values remain explicit rather than inferred.

NotableJetBrains' first-party Apache-2.0 12B/2.5B-active MoE reasoning and software-agent release; curation reflects developer relevance and official source availability, not independent OMW benchmark results.Curation method →

Source repository ↗Compare this model →History & diff →Machine-readable JSON ↗Field-verified 2026-10-11

Evidence statusSource-first verified

Last verified11 Oct 2026

Full field verification11 Oct 2026

Source policy →Methodology →

FRESHNESS & VERIFICATION

Current evidence, dated honestly.

A verification check does not pretend the model changed. Open Model Weights updates the verification date after a real primary-source check, while factual-update dates move only when retained source evidence changes.

Last verified: 11 Oct 2026
Last factual update: No change observed
Repository created: 20 Sep 2026

View observed history →View evidence JSON →View model JSON →

CONFLICT INTELLIGENCE

Claims stay attached to evidence class.

No active comparable-source conflict detectedThis is not a claim that every possible source agrees; it covers the comparable fields currently checked.

Publisher claims6

Source observed4

OMW derived3

OMW measured0

Conflict Intelligence →Conflict JSON ↗Evidence IDs ↗OMW measurement policy →

+ Save to my shortlist Monitor changes →Local browser monitoring · no background email alerts

MODEL INTELLIGENCE · SOURCE-FIRST

What is Mellum2.1-12B-A2.5B-Thinking?

OMW evidence review11 Oct 2026

Open Model Weights records Mellum2.1-12B-A2.5B-Thinking as a 12.1499B-parameter text open-weight model in the Mellum2.1 family, with JetBrains listed as the developer. The checked source repository provides 6 recognized weight artifacts, format evidence for Safetensors and a verified context window of 131,072 tokens. Values that are not evidenced in the checked sources remain explicitly undisclosed or unknown.

The repository declares apache-2.0. Commercial use allowed under apache-2.0 conditions. Open Model Weights reports the checked license evidence and classification; this is not legal advice.

The checked sources declare JetBrains/Mellum2-12B-A2.5B-Base as lineage evidence. Training recipe status: training-described-in-model-card; data disclosure status: described-in-model-card.

Source repository ↗Model card ↗Configuration ↗

DEPLOYMENT PROFILE

Weight memory, without pretending it is a deployment guarantee.

These bars visualize weight-only decimal-GB estimates. They exclude KV cache, activations, runtime overhead, optimizer state and sharding.

WEIGHT-ONLY MEMORY

BF16 / FP16~24.3 GB

FP8 / INT8~12.2 GB

INT4~6.1 GB

FIELD EVIDENCE MAP

WeightsVerified

LicenseVerified

Commercial useAllowed

ContextVerified

FormatsVerified

LineageDeclared

Training recipeTraining described in model card

Training dataDescribed in model card

RuntimeSource-derived · not runtime-tested

LICENSE & USE

apache-2.0

Commercial use allowed under apache-2.0 conditions

Declared licenseapache-2.0

ClassificationAllowed

VerificationDeclared metadata checked

This section summarizes the checked repository evidence. It is not legal advice.

LINEAGE & PROVENANCE

What the checked sources disclose — and what they do not.

Open Model Weights does not infer a hidden base model or training corpus when the checked sources do not declare one.

LINEAGE

BASE / PARENTJetBrains/Mellum2-12B-A2.5B-BaseDeclared

base_model

CURRENT RECORDMellum2.1-12B-A2.5B-ThinkingMellum2.1

TRAINING DISCLOSURE

Training recipeTraining described in model card

Training dataDescribed in model card

FamilyMellum2.1

RUNTIME SIGNALS

Compatibility claims stay attached to their evidence level.

Declared and model-card-mentioned runtimes are discovery signals. They are not treated as Open Model Weights runtime tests unless explicitly measured.

Declaredtransformers

MentionedOllama

MentionedTransformers

Mentionedllama.cpp

MentionedvLLM

OMW runtime testNot performed

EVIDENCE TRAIL

Sources and observed history.

This is where the article remains auditable: source links on one side, the registry's observed change history on the other.

PrimaryModel Repositoryhttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-ThinkingInspect source ↗PrimaryModel Apihttps://huggingface.co/api/models/JetBrains/Mellum2.1-12B-A2.5B-ThinkingInspect source ↗PrimaryModel Cardhttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-Thinking/blob/main/README.mdInspect source ↗PrimaryConfighttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-Thinking/blob/main/config.jsonInspect source ↗

2026-10-11

Field-by-field verification

Checked Hugging Face API metadata, exact repository file list, model card and config when accessible.

01 · WEIGHTS

Exact repository artifacts

Weightsverified-available

Accesspublic

RepositoryJetBrains/Mellum2.1-12B-A2.5B-Thinking

Recognized weight files6

Show all 6 exact weight files

HF API file listing ↗

02 · LICENSE

License & commercial use

Declared licenseapache-2.0

License IDapache-2.0

Commercial useCommercial use allowed under apache-2.0 conditions

Repository license filesNone observed

Classification describes the checked license terms; it is not legal advice.

03 · HARDWARE

Weight-memory estimate

BF16 / FP16~24.3 GB

FP8 / INT8~12.2 GB

INT4~6.1 GB

Weight-only decimal-GB estimate from total parameter count; excludes KV cache, activations, runtime overhead, optimizer state and sharding.

04 · FORMATS

Formats & precision evidence

Safetensors

BF16: not observedFP16: not observedFP8: not observedINT8: not observedINT4: not observedGGUF: not observed

“Not observed” means no matching repository artifact/name/dtype signal was found; it does not prove no third-party conversion exists.

05 · LINEAGE

Base model & family

FamilyMellum2.1

VariantThinking

Declared base modelJetBrains/Mellum2-12B-A2.5B-Base

Relationbase_model

06 · TRAINING ASSETS

Recipe & data disclosure

Training recipetraining-described-in-model-card

Data disclosuredescribed-in-model-card

EvaluationsNot classified by automated verifier

Intermediate checkpointsNot classified by automated verifier

07 · RUNTIME SUPPORT

Declared, mentioned and externally evidenced runtimes

Declared librarytransformers

Declared/taggedtransformers

Mentioned in model cardOllama, Transformers, llama.cpp, vLLM

Artifact signalsNone

External primary runtime evidenceNone

Tested by Open Model WeightsNo — source-derived support only

Open Model Weights separates model-repository evidence from external runtime-release evidence. An external support statement does not change the official model repository's weight formats and does not imply an Open Model Weights inference benchmark.

08 · SOURCES

Field evidence

Primary / declared sources4

Repository revision92ddae9fc766

Source policyHow evidence is classified →

model_repositoryhttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-Thinking

model_apihttps://huggingface.co/api/models/JetBrains/Mellum2.1-12B-A2.5B-Thinking

model_cardhttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-Thinking/blob/main/README.md

confighttps://huggingface.co/JetBrains/Mellum2.1-12B-A2.5B-Thinking/blob/main/config.json

09 · VERIFICATION HISTORY

Checked, not assumed

2026-10-11

Field-by-field verification

Checked Hugging Face API metadata, exact repository file list, model card and config when accessible.

licenseverified

commercial useclassified

contextverified

weight filesverified

formatsverified

base modeldeclared

training recipetraining-described-in-model-card

data disclosuredescribed-in-model-card

runtime supportsource-derived-not-runtime-tested