# Claude Sonnet 4.5 vs Mellum2-12B-A2.5B-Instruct

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

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

- Shared sourced benchmarks: 1
- HTML indexing: indexable
- Ranking lane: BenchAlign v5

## Quick Verdict

Evidence is too thin for a benchmark verdict: Claude Sonnet 4.5 and Mellum2-12B-A2.5B-Instruct share only 1 sourced benchmark row.

## Summary

- Only 1 shared sourced benchmark row is available. That is not enough for a broad capability verdict, so this mirror does not name an overall winner.
- Claude Sonnet 4.5 has the larger published context window at 200K.

## Model Snapshot

| Property | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct |
|----------|----------|----------|
| Creator | Anthropic | JetBrains |
| Type | Proprietary | Open Weight |
| Reasoning | Non-Reasoning | Non-Reasoning |
| Context | 200K | 128K |
| Independent public score (not head-to-head) | 53.74 | null |
| Benchmarks Covered | 11 | 6 |
| Pricing (input/output) | $3.00 / $15.00 | N/A |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: 44.6 (Estimated · #100/151)
- Mellum2-12B-A2.5B-Instruct public-lane score: 47.8 (Estimated · #82/151)

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 50% | Coming soon | Coming soon |
| OSWorld-Verified | 61.4% | Coming soon | Coming soon |
| VITA-Bench | 17.0% | Coming soon | Coming soon |
| Gert Labs | 48.51% | Coming soon | Coming soon |
| JobBench | 27.7% | Coming soon | Coming soon |
| BFCL v4 | Coming soon | 44.2% | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: 51 (Estimated · #67/183)
- Mellum2-12B-A2.5B-Instruct public-lane score: Coming soon

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 77.2% | Coming soon | Coming soon |
| LiveCodeBench v6 | Coming soon | 37.2% | Coming soon |

### Reasoning

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: 19.1 (Unranked · 1 rankable row)
- Mellum2-12B-A2.5B-Instruct public-lane score: Coming soon

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| ARC-AGI-2 | 13.6% | Coming soon | Coming soon |

### Knowledge

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: 51.5 (Estimated · #81/181)
- Mellum2-12B-A2.5B-Instruct public-lane score: 48.1 (Estimated · #103/181)

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 83.4% | 40.9% | Claude Sonnet 4.5 |
| MMLU-Redux | Coming soon | 78.1% | Coming soon |
| GPQA-D | Coming soon | 40.9% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: Coming soon
- Mellum2-12B-A2.5B-Instruct public-lane score: Coming soon

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| IFEval | Coming soon | 75.8% | Coming soon |

### Mathematics

- Winner: Insufficient shared evidence
- Claude Sonnet 4.5 public-lane score: 34.8 (Unranked · 2 rankable rows)
- Mellum2-12B-A2.5B-Instruct public-lane score: Coming soon

| Benchmark | Claude Sonnet 4.5 | Mellum2-12B-A2.5B-Instruct | Winner |
|-----------|-----------|-----------|--------|
| AIME 2025 | 87% | Coming soon | Coming soon |
| FrontierMath v2 (Tiers 1-3) | 13.495% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 4.167% | Coming soon | Coming soon |

## FAQ

### Is there enough evidence to pick between Claude Sonnet 4.5 and Mellum2-12B-A2.5B-Instruct?

Not yet. The models share only 1 sourced benchmark row, 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

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

## Explore More

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