# Mellum2.1-12B-A2.5B-Thinking vs Solar Open 2

> Side-by-side benchmark comparison for Mellum2.1-12B-A2.5B-Thinking and Solar Open 2 across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/mellum2-1-12b-a2-5b-thinking-vs-solar-open-2
- 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: Mellum2.1-12B-A2.5B-Thinking and Solar Open 2 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.
- Solar Open 2 has the larger published context window at 1M.

## Model Snapshot

| Property | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 |
|----------|----------|----------|
| Creator | JetBrains | Upstage |
| Type | Open Weight | Open Weight |
| Reasoning | Reasoning | Reasoning |
| Context | 128K | 1M |
| Independent public score (not head-to-head) | null | null |
| Benchmarks Covered | 7 | 11 |
| Pricing (input/output) | $0.00 / $0.00 | $0.00 / $0.00 |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- Solar Open 2 public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.1 | 17.4% | Coming soon | Coming soon |
| terminalBenchHard | Coming soon | 28.3% | Coming soon |
| APEX-Agents | Coming soon | 16.6% | Coming soon |
| MCP Atlas | Coming soon | 58.2% | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- Solar Open 2 public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 | Winner |
|-----------|-----------|-----------|--------|
| LiveCodeBench v6 | 82.0% | 92.4% | Solar Open 2 |
| SWE-bench Verified | 47% | 70.4% | Solar Open 2 |
| SWE-bench Pro | 28% | Coming soon | Coming soon |

### Knowledge

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- Solar Open 2 public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 | Winner |
|-----------|-----------|-----------|--------|
| MMLU-Redux | 87.8% | Coming soon | Coming soon |
| GPQA-D | 64.6% | 86.3% | Solar Open 2 |
| MMLU-Pro | Coming soon | 86.2% | Coming soon |
| HLE w/o tools | Coming soon | 28.8% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- Solar Open 2 public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 | Winner |
|-----------|-----------|-----------|--------|
| IFEval | 90.6% | Coming soon | Coming soon |
| IFBench | Coming soon | 80% | Coming soon |

### Mathematics

- Winner: Insufficient shared evidence
- Mellum2.1-12B-A2.5B-Thinking public-lane score: Coming soon
- Solar Open 2 public-lane score: Coming soon

| Benchmark | Mellum2.1-12B-A2.5B-Thinking | Solar Open 2 | Winner |
|-----------|-----------|-----------|--------|
| HMMT Feb 2026 | Coming soon | 93.9% | Coming soon |
| AIME26 | Coming soon | 95.7% | Coming soon |

## FAQ

### Is there enough evidence to pick between Mellum2.1-12B-A2.5B-Thinking and Solar Open 2?

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

- [Mellum2.1-12B-A2.5B-Thinking vs Claude Opus 5.5](/compare/claude-opus-5-5-vs-mellum2-1-12b-a2-5b-thinking)
- [Solar Open 2 vs Claude Opus 5.5](/compare/claude-opus-5-5-vs-solar-open-2)
- [Mellum2.1-12B-A2.5B-Thinking vs GPT-6 Astra](/compare/gpt-6-astra-vs-mellum2-1-12b-a2-5b-thinking)
- [Solar Open 2 vs GPT-6 Astra](/compare/gpt-6-astra-vs-solar-open-2)

## Explore More

- [Mellum2.1-12B-A2.5B-Thinking profile](/models/mellum2-1-12b-a2-5b-thinking)
- [Solar Open 2 profile](/models/solar-open-2)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)