# Mellum2-12B-A2.5B-Thinking vs o1

> Side-by-side benchmark comparison for Mellum2-12B-A2.5B-Thinking and o1 across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/mellum2-12b-a2-5b-thinking-vs-o1
- Last updated: September 4, 2026

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

## Quick Verdict

Evidence is too thin for a benchmark verdict: Mellum2-12B-A2.5B-Thinking and o1 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.
- o1 has the larger published context window at 200K.

## Model Snapshot

| Property | Mellum2-12B-A2.5B-Thinking | o1 |
|----------|----------|----------|
| Creator | JetBrains | OpenAI |
| Type | Open Weight | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | 128K | 200K |
| Independent public score (not head-to-head) | null | 47.89 |
| Benchmarks Covered | 6 | 4 |
| Pricing (input/output) | N/A | $15.00 / $60.00 |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.3 (Estimated · #76/151)
- o1 public-lane score: Coming soon

| Benchmark | Mellum2-12B-A2.5B-Thinking | o1 | Winner |
|-----------|-----------|-----------|--------|
| BFCL v4 | 45.6% | Coming soon | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon
- o1 public-lane score: 46.1 (Estimated · #101/183)

| Benchmark | Mellum2-12B-A2.5B-Thinking | o1 | Winner |
|-----------|-----------|-----------|--------|
| LiveCodeBench v6 | 69.9% | Coming soon | Coming soon |

### Reasoning

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon
- o1 public-lane score: 66.5 (Unranked · 2 rankable rows)

### Knowledge

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.8 (Estimated · #96/181)
- o1 public-lane score: 46.6 (Supported · #106/181)

| Benchmark | Mellum2-12B-A2.5B-Thinking | o1 | Winner |
|-----------|-----------|-----------|--------|
| MMLU-Redux | 86.2% | Coming soon | Coming soon |
| GPQA | 57.6% | 75.7% | o1 |
| GPQA-D | 57.6% | Coming soon | Coming soon |
| MMLU | Coming soon | 91.8% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon
- o1 public-lane score: 85.7 (#39/120)

| Benchmark | Mellum2-12B-A2.5B-Thinking | o1 | Winner |
|-----------|-----------|-----------|--------|
| IFEval | 76.5% | 92.2% | o1 |

### Mathematics

- Winner: Insufficient shared evidence
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon
- o1 public-lane score: 32.6 (Unranked · 1 rankable row)

| Benchmark | Mellum2-12B-A2.5B-Thinking | o1 | Winner |
|-----------|-----------|-----------|--------|
| FrontierMath v2 (Tiers 1-3) | Coming soon | 9.310% | Coming soon |

## FAQ

### Is there enough evidence to pick between Mellum2-12B-A2.5B-Thinking and o1?

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

- [Mellum2-12B-A2.5B-Thinking vs Mellum2-12B-A2.5B-Instruct](/compare/mellum2-12b-a2-5b-instruct-vs-mellum2-12b-a2-5b-thinking)
- [o1 vs Mellum2-12B-A2.5B-Instruct](/compare/mellum2-12b-a2-5b-instruct-vs-o1)
- [Mellum2-12B-A2.5B-Thinking vs o1-preview](/compare/mellum2-12b-a2-5b-thinking-vs-o1-preview)
- [o1 vs o1-preview](/compare/o1-vs-o1-preview)

## Explore More

- [Mellum2-12B-A2.5B-Thinking profile](/models/mellum2-12b-a2-5b-thinking)
- [o1 profile](/models/o1)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)