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

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

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

- Shared sourced benchmarks: 3
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.8

## Quick Verdict

Evidence is too thin for a benchmark verdict: Claude Mythos 5 and Mellum2.1-12B-A2.5B-Thinking share only 3 sourced benchmark rows.

## Summary

- Only 3 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.
- Claude Mythos 5 has the larger published context window at 1M+.

## Model Snapshot

| Property | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking |
|----------|----------|----------|
| Creator | Anthropic | JetBrains |
| Type | Proprietary | Open Weight |
| Reasoning | Reasoning | Reasoning |
| Context | 1M+ | 128K |
| Independent public score (not head-to-head) | null | null |
| Benchmarks Covered | 15 | 7 |
| Pricing (input/output) | $10.00 / $50.00 | $0.00 / $0.00 |

## Category Breakdown

### Agentic

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

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.1 | 88.0% | 17.4% | Claude Mythos 5 |
| OSWorld-Verified | 85% | Coming soon | Coming soon |
| BrowseComp | 88% | Coming soon | Coming soon |
| CyberGym | 83.8% | Coming soon | Coming soon |

### Coding

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

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Verified | 95.5% | 47% | Claude Mythos 5 |
| SWE-bench Pro | 80.3% | 28% | Claude Mythos 5 |
| Terminal-Bench 2.1 | 88.0% | Coming soon | Coming soon |
| LiveCodeBench v6 | Coming soon | 82.0% | Coming soon |

### Multimodal & Grounded

- Winner: Insufficient shared evidence
- Claude Mythos 5 public-lane score: 86.2 (Unranked · 3 rankable rows)
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Multimodal | 54.9% | Coming soon | Coming soon |
| CharXiv | 93.5% | Coming soon | Coming soon |
| CharXiv w/o tools | 88.9% | Coming soon | Coming soon |

### Knowledge

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

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 94.1% | Coming soon | Coming soon |
| HLE | 64.5% | Coming soon | Coming soon |
| HLE w/o tools | 59% | Coming soon | Coming soon |
| MMLU-Redux | Coming soon | 87.8% | Coming soon |
| GPQA-D | Coming soon | 64.6% | Coming soon |

### Multilingual

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

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| SWE Multilingual | 92.2% | Coming soon | Coming soon |

### Instruction Following

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

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

### Mathematics

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

| Benchmark | Claude Mythos 5 | Mellum2.1-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| USAMO 2026 | 97.6% | Coming soon | Coming soon |

## FAQ

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

Not yet. The models share only 3 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

- [Claude Mythos 5 vs Claude Mythos 5.1](/compare/claude-mythos-5-vs-claude-mythos-5-1)
- [Mellum2.1-12B-A2.5B-Thinking vs Claude Mythos 5.1](/compare/claude-mythos-5-1-vs-mellum2-1-12b-a2-5b-thinking)
- [Claude Mythos 5 vs Claude Mythos Preview](/compare/claude-mythos-5-vs-claude-mythos-preview)
- [Mellum2.1-12B-A2.5B-Thinking vs Claude Mythos Preview](/compare/claude-mythos-preview-vs-mellum2-1-12b-a2-5b-thinking)

## Explore More

- [Claude Mythos 5 profile](/models/claude-mythos-5)
- [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)