# Claude Opus 4.5 vs Mellum2-12B-A2.5B-Thinking

> Side-by-side benchmark comparison for Claude Opus 4.5 and Mellum2-12B-A2.5B-Thinking across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

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

- Shared sourced benchmarks: 4
- HTML indexing: indexable
- Ranking lane: BenchAlign v5

## Quick Verdict

Pick Claude Opus 4.5 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only makes more sense when its price, context window, or workload-specific category wins matter more than the overall score.

## Summary

- Claude Opus 4.5 leads overall 60.24 to 52.
- The clearest category separation is in knowledge, where the averages are 55.4 for Claude Opus 4.5 and 48.8 for Mellum2-12B-A2.5B-Thinking.
- The biggest single benchmark swing is GPQA in Knowledge, with scores of 87% and 57.6%.
- Claude Opus 4.5 also has the larger context window at 200K.

## Model Snapshot

| Property | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking |
|----------|----------|----------|
| Creator | Anthropic | JetBrains |
| Type | Proprietary | Open Weight |
| Reasoning | Non-Reasoning | Reasoning |
| Context | 200K | 128K |
| Overall Score | 60.24 | null |
| Benchmarks Covered | 45 | 6 |
| Pricing (input/output) | $5.00 / $25.00 | N/A |

## Category Breakdown

### Agentic

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 44.4 (Estimated · #101/151)
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.3 (Estimated · #76/151)

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 59.3% | Coming soon | Coming soon |
| OSWorld-Verified | 66.3% | Coming soon | Coming soon |
| OSWorld | 66.3% | Coming soon | Coming soon |
| Claw-Eval | 59.6% | Coming soon | Coming soon |
| QwenClawBench | 52.3% | Coming soon | Coming soon |
| τ³-bench results | 70.2% | Coming soon | Coming soon |
| VITA-Bench | 23.3% | Coming soon | Coming soon |
| DeepPlanning | 26.4% | Coming soon | Coming soon |
| Toolathlon | 43.5% | Coming soon | Coming soon |
| MCP Atlas | 42.3% | Coming soon | Coming soon |
| MCP-Tasks | 71.8% | Coming soon | Coming soon |
| WideResearch | 76.4% | Coming soon | Coming soon |
| CyberGym | 50.6% | Coming soon | Coming soon |
| Gert Labs | 64.23% | Coming soon | Coming soon |
| JobBench | 32.3% | Coming soon | Coming soon |
| BFCL v4 | Coming soon | 45.6% | Coming soon |

### Coding

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 55.1 (Supported · #42/183)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 80.9% | Coming soon | Coming soon |
| LiveCodeBench v6 | 84.8% | 69.9% | Claude Opus 4.5 |
| SWE-bench Pro | 57.1% | Coming soon | Coming soon |
| SWE Multilingual | 77.5% | Coming soon | Coming soon |
| NL2Repo | 43.2% | Coming soon | Coming soon |

### Multimodal & Grounded

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 23.5 (#46/48)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| MMMU-Pro | 70.6% | Coming soon | Coming soon |
| MathVision | 74.3% | Coming soon | Coming soon |
| CharXiv | 68.5% | Coming soon | Coming soon |
| VideoMMMU | 84.4% | Coming soon | Coming soon |
| ScreenSpot Pro | 45.7% | Coming soon | Coming soon |
| V* | 67.0% | Coming soon | Coming soon |

### Reasoning

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 72.1 (Unranked · 4 rankable rows)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| LongBench v2 | 64.4% | Coming soon | Coming soon |
| AI-Needle | 74% | Coming soon | Coming soon |

### Knowledge

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 55.4 (Estimated · #60/181)
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.8 (Estimated · #96/181)

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 87% | 57.6% | Claude Opus 4.5 |
| SuperGPQA | 70.6% | Coming soon | Coming soon |
| MMLU-Pro | 89.5% | Coming soon | Coming soon |
| MMLU-Redux | 96.6% | 86.2% | Claude Opus 4.5 |
| C-Eval | 92.2% | Coming soon | Coming soon |
| HLE | 30.8% | Coming soon | Coming soon |
| GPQA-D | Coming soon | 57.6% | Coming soon |

### Instruction Following

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 39.5 (#103/120)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| IFEval | 90.9% | 76.5% | Claude Opus 4.5 |
| IFBench | 58% | Coming soon | Coming soon |

### Multilingual

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 82.9 (#2/12)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| MMLU-ProX | 85.7% | Coming soon | Coming soon |
| NOVA-63 | 56.7% | Coming soon | Coming soon |

### Mathematics

- Winner: Coming soon
- Claude Opus 4.5 public-lane score: 58.3 (#6/7)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.5 | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| AIME26 | 95.1% | Coming soon | Coming soon |
| HMMT Feb 2025 | 92.9% | Coming soon | Coming soon |
| HMMT Nov 2025 | 93.3% | Coming soon | Coming soon |
| HMMT Feb 2026 | 85.3% | Coming soon | Coming soon |
| MMAnswerBench | 84.0% | Coming soon | Coming soon |
| FrontierMath v2 (Tiers 1-3) | 20.690% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 4.167% | Coming soon | Coming soon |

## FAQ

### Which is better overall, Claude Opus 4.5 or Mellum2-12B-A2.5B-Thinking?

Claude Opus 4.5 is ahead overall on BenchLM right now.

### Where is the biggest gap between Claude Opus 4.5 and Mellum2-12B-A2.5B-Thinking?

The widest category gap is in knowledge, where the averages are 55.4 for Claude Opus 4.5 and 48.8 for Mellum2-12B-A2.5B-Thinking.

### How many benchmarks does Claude Opus 4.5 cover on BenchLM?

Claude Opus 4.5 currently has 45 sourced benchmark scores on BenchLM.

### How many benchmarks does Mellum2-12B-A2.5B-Thinking cover on BenchLM?

Mellum2-12B-A2.5B-Thinking currently has 6 sourced benchmark scores on BenchLM.

## Related Comparisons

- [Claude Opus 4.5 vs Claude Opus 4.5 Thinking](/compare/claude-opus-4-5-vs-claude-opus-4-5-thinking)
- [Mellum2-12B-A2.5B-Thinking vs Claude Opus 4.5 Thinking](/compare/claude-opus-4-5-thinking-vs-mellum2-12b-a2-5b-thinking)
- [Claude Opus 4.5 vs Mellum2-12B-A2.5B-Instruct](/compare/claude-opus-4-5-vs-mellum2-12b-a2-5b-instruct)
- [Mellum2-12B-A2.5B-Thinking vs Mellum2-12B-A2.5B-Instruct](/compare/mellum2-12b-a2-5b-instruct-vs-mellum2-12b-a2-5b-thinking)

## Explore More

- [Claude Opus 4.5 profile](/models/claude-opus-4-5)
- [Mellum2-12B-A2.5B-Thinking profile](/models/mellum2-12b-a2-5b-thinking)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)