# Mellum2.1-12B-A2.5B-Thinking vs o3-mini

> Side-by-side benchmark comparison for Mellum2.1-12B-A2.5B-Thinking and o3-mini across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/mellum2-1-12b-a2-5b-thinking-vs-o3-mini
- Last updated: October 8, 2026

- Shared sourced benchmarks: 2
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.8

## Quick Verdict

Evidence is too thin for a benchmark verdict: Mellum2.1-12B-A2.5B-Thinking and o3-mini share only 2 sourced benchmark rows.

## Summary

- Only 2 shared sourced benchmark rows are available. That is not enough for a broad capability verdict, so this mirror does not name an overall winner.
- Mellum2.1-12B-A2.5B-Thinking has the lower published output-token price.
- o3-mini has the larger published context window at 200K.

## Model Snapshot

| Property | Mellum2.1-12B-A2.5B-Thinking | o3-mini |
|----------|----------|----------|
| Creator | JetBrains | OpenAI |
| Type | Open Weight | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | 128K | 200K |
| Independent public score (not head-to-head) | null | 40.19 |
| Benchmarks Covered | 7 | 5 |
| Pricing (input/output) | $0.00 / $0.00 | $1.10 / $4.40 |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- o3-mini public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | o3-mini | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.1 | 17.4% | Coming soon | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- o3-mini public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | o3-mini | Winner |
|-----------|-----------|-----------|--------|
| LiveCodeBench v6 | 82.0% | Coming soon | Coming soon |
| SWE-bench Verified | 47% | 49.3% | o3-mini |
| SWE-bench Pro | 28% | Coming soon | Coming soon |

### Knowledge

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- o3-mini public-lane score: 35.4 (Supported · #119/174)

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | o3-mini | Winner |
|-----------|-----------|-----------|--------|
| MMLU-Redux | 87.8% | Coming soon | Coming soon |
| GPQA-D | 64.6% | Coming soon | Coming soon |
| MMLU | Coming soon | 86.9% | Coming soon |
| GPQA | Coming soon | 77.2% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- o3-mini public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | o3-mini | Winner |
|-----------|-----------|-----------|--------|
| IFEval | 90.6% | 93.9% | o3-mini |

### Mathematics

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- o3-mini public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | o3-mini | Winner |
|-----------|-----------|-----------|--------|
| AIME 2024 | Coming soon | 87.3% | Coming soon |

## FAQ

### Is there enough evidence to pick between Mellum2.1-12B-A2.5B-Thinking and o3-mini?

Not yet. The models share only 2 sourced benchmark rows, so this mirror reports the available measurements and metadata without naming a broad winner.

### What can I compare safely on this page?

Published pricing, context windows, model type, and individual shared benchmark rows are directly comparable. Independent overall scores and non-overlapping benchmark coverage are labeled separately and should not be read as a controlled head-to-head result.

## Related Comparisons

- [Mellum2.1-12B-A2.5B-Thinking vs o3-pro](/compare/mellum2-1-12b-a2-5b-thinking-vs-o3-pro)
- [o3-mini vs o3-pro](/compare/o3-mini-vs-o3-pro)
- [Mellum2.1-12B-A2.5B-Thinking vs o3](/compare/mellum2-1-12b-a2-5b-thinking-vs-o3)
- [o3-mini vs o3](/compare/o3-vs-o3-mini)

## Explore More

- [Mellum2.1-12B-A2.5B-Thinking profile](/models/mellum2-1-12b-a2-5b-thinking)
- [o3-mini profile](/models/o3-mini)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)