# Claude Opus 4.8 vs Mellum2.1-12B-A2.5B-Thinking

> Side-by-side benchmark comparison for Claude Opus 4.8 and Mellum2.1-12B-A2.5B-Thinking across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/claude-opus-4-8-vs-mellum2-1-12b-a2-5b-thinking
- Last updated: October 8, 2026

- Shared sourced benchmarks: 4
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.8

## Quick Verdict

Pick Claude Opus 4.8 if you want the stronger benchmark profile. Mellum2.1-12B-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 4.8 leads overall 69.04 to 37.
- The biggest single benchmark swing is Terminal-Bench 2.1 in Agentic, with scores of 74.6% and 17.4%.
- Mellum2.1-12B-A2.5B-Thinking is the cheaper option on output tokens, which matters if you expect large responses or heavy interactive use.
- Claude Opus 4.8 also has the larger context window at 1M.

## Model Snapshot

| Property | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking |
|----------|----------|----------|
| Creator | Anthropic | JetBrains |
| Type | Proprietary | Open Weight |
| Reasoning | Reasoning | Reasoning |
| Context | 1M | 128K |
| Overall Score | 69.04 | null |
| Benchmarks Covered | 40 | 7 |
| Pricing (input/output) | $5.00 / $25.00 | $0.00 / $0.00 |

## Category Breakdown

### Agentic

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 61.8 (Supported · #20/122)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 3.0 | 21.1% | Coming soon | Coming soon |
| Terminal-Bench 2.1 | 74.6% | 17.4% | Claude Opus 4.8 |
| BrowseComp | 84.3% | Coming soon | Coming soon |
| DeepSearchQA | 93.1% | Coming soon | Coming soon |
| OSWorld-Verified | 83.4% | Coming soon | Coming soon |
| Finance Agent v2 | 53.9% | Coming soon | Coming soon |
| MCP Atlas | 82.2% | Coming soon | Coming soon |
| Toolathlon | 59.9% | Coming soon | Coming soon |
| Gert Labs | 72.97% | Coming soon | Coming soon |
| ResearchClawBench | 21.1% | Coming soon | Coming soon |
| OSWorld 2.0 | 20.6% | Coming soon | Coming soon |
| Terminal-Bench 2.1 (Vals) | 71.9% | Coming soon | Coming soon |

### Coding

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 61.1 (Supported · #18/146)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 88.6% | 47% | Claude Opus 4.8 |
| SWE-bench Pro | 69.2% | 28% | Claude Opus 4.8 |
| SWE Multilingual | 84.4% | Coming soon | Coming soon |
| SWE Multimodal | 38.4% | Coming soon | Coming soon |
| Terminal-Bench 2.1 | 74.6% | Coming soon | Coming soon |
| cursorBench31 | 58.4% | Coming soon | Coming soon |
| CursorBench 3.2 | 62.3% | Coming soon | Coming soon |
| FrontierCode 1.1 Main | 46.5% | Coming soon | Coming soon |
| LiveCodeBench (Vals) | 87.8% | Coming soon | Coming soon |
| SWE-bench (Vals) | 88.6% | Coming soon | Coming soon |
| PostTrainBench v1.1 | 32.9% | Coming soon | Coming soon |
| LiveCodeBench v6 | Coming soon | 82.0% | Coming soon |

### Reasoning

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 59.1 (#23/28)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| ARC-AGI-2 | 72.1% | Coming soon | Coming soon |
| ARC-AGI-3 | 1.5% | Coming soon | Coming soon |
| ARC-AGI-1 | 92.50% | Coming soon | Coming soon |

### Multimodal & Grounded

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 87.7 (#7/49)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| OfficeQA Pro | 66.2% | Coming soon | Coming soon |
| ScreenSpot Pro | 87.9% | Coming soon | Coming soon |
| CharXiv | 89.9% | Coming soon | Coming soon |
| CharXiv w/o tools | 80.5% | Coming soon | Coming soon |

### Knowledge

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 69.3 (Supported · #15/174)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 93.6% | Coming soon | Coming soon |
| GPQA-D | 93.6% | 64.6% | Claude Opus 4.8 |
| HLE | 57.9% | Coming soon | Coming soon |
| HLE w/o tools | 49.8% | Coming soon | Coming soon |
| GPQA Diamond (Vals) | 92.4% | Coming soon | Coming soon |
| MMLU-Pro (Vals) | 89.6% | Coming soon | Coming soon |
| MMLU-Redux | Coming soon | 87.8% | Coming soon |

### Multilingual

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: Coming soon
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| INCLUDE | 87.6% | Coming soon | Coming soon |

### Instruction Following

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 74 (#60/125)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| IFEval | Coming soon | 90.6% | Coming soon |

### Mathematics

- Winner: Not comparable
- Claude Opus 4.8 public-lane score: 65.2 (#2/7)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Opus 4.8 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| USAMO 2026 | 96.7% | Coming soon | Coming soon |
| FrontierMath v2 (Tiers 1-3) | 47.241% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 31.250% | Coming soon | Coming soon |

## FAQ

### Which is better overall, Claude Opus 4.8 or Mellum2.1-12B-A2.5B-Thinking?

Claude Opus 4.8 is ahead overall on BenchLM right now.

### How many benchmarks does Claude Opus 4.8 cover on BenchLM?

Claude Opus 4.8 currently has 40 sourced benchmark scores on BenchLM.

### How many benchmarks does Mellum2.1-12B-A2.5B-Thinking cover on BenchLM?

Mellum2.1-12B-A2.5B-Thinking currently has 7 sourced benchmark scores on BenchLM.

## Related Comparisons

- [Claude Opus 4.8 vs Claude Opus 5.5](/compare/claude-opus-4-8-vs-claude-opus-5-5)
- [Mellum2.1-12B-A2.5B-Thinking vs Claude Opus 5.5](/compare/claude-opus-5-5-vs-mellum2-1-12b-a2-5b-thinking)
- [Claude Opus 4.8 vs GPT-6 Astra](/compare/claude-opus-4-8-vs-gpt-6-astra)
- [Mellum2.1-12B-A2.5B-Thinking vs GPT-6 Astra](/compare/gpt-6-astra-vs-mellum2-1-12b-a2-5b-thinking)

## Explore More

- [Claude Opus 4.8 profile](/models/claude-opus-4-8)
- [Mellum2.1-12B-A2.5B-Thinking profile](/models/mellum2-1-12b-a2-5b-thinking)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)