# GPT-5.4 nano vs Mellum2-12B-A2.5B-Thinking

> Side-by-side benchmark comparison for GPT-5.4 nano and Mellum2-12B-A2.5B-Thinking across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/gpt-5-4-nano-vs-mellum2-12b-a2-5b-thinking
- 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: GPT-5.4 nano and Mellum2-12B-A2.5B-Thinking 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.
- GPT-5.4 nano has the larger published context window at 400K.

## Model Snapshot

| Property | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking |
|----------|----------|----------|
| Creator | OpenAI | JetBrains |
| Type | Proprietary | Open Weight |
| Reasoning | Reasoning | Reasoning |
| Context | 400K | 128K |
| Independent public score (not head-to-head) | 62.19 | null |
| Benchmarks Covered | 18 | 6 |
| Pricing (input/output) | $0.20 / $1.25 | N/A |

## Category Breakdown

### Agentic

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 37.3 (Supported · #127/151)
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.3 (Estimated · #76/151)

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 2.0 | 46.3% | Coming soon | Coming soon |
| OSWorld-Verified | 39% | Coming soon | Coming soon |
| MCP Atlas | 56.1% | Coming soon | Coming soon |
| Toolathlon | 35.5% | Coming soon | Coming soon |
| τ²-bench results | 92.5% | Coming soon | Coming soon |
| Terminal-Bench 2.1 (Vals) | 41.6% | Coming soon | Coming soon |
| BFCL v4 | Coming soon | 45.6% | Coming soon |

### Coding

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 37.4 (Supported · #150/183)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| Vibe Code Bench | 26.10% | Coming soon | Coming soon |
| LiveCodeBench (Vals) | 84.0% | Coming soon | Coming soon |
| SWE-bench (Vals) | 69.8% | Coming soon | Coming soon |
| LiveCodeBench v6 | Coming soon | 69.9% | Coming soon |

### Multimodal & Grounded

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 23.8 (#45/48)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| MMMU-Pro | 66.1% | Coming soon | Coming soon |
| MMMU-Pro w/ Python | 69.5% | Coming soon | Coming soon |

### Reasoning

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 72.8 (Unranked · 2 rankable rows)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

### Knowledge

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 48.5 (Supported · #99/181)
- Mellum2-12B-A2.5B-Thinking public-lane score: 48.8 (Estimated · #96/181)

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 82.8% | 57.6% | GPT-5.4 nano |
| HLE | 37.7% | Coming soon | Coming soon |
| HLE w/o tools | 24.3% | Coming soon | Coming soon |
| GPQA Diamond (Vals) | 77.5% | Coming soon | Coming soon |
| MMLU-Pro (Vals) | 77.2% | Coming soon | Coming soon |
| MMLU-Redux | Coming soon | 86.2% | Coming soon |
| GPQA-D | Coming soon | 57.6% | Coming soon |

### Instruction Following

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 92.9 (#9/120)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| IFEval | Coming soon | 76.5% | Coming soon |

### Mathematics

- Winner: Insufficient shared evidence
- GPT-5.4 nano public-lane score: 43.9 (Unranked · 2 rankable rows)
- Mellum2-12B-A2.5B-Thinking public-lane score: Coming soon

| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Thinking | Winner |
|-----------|-----------|-----------|--------|
| FrontierMath v2 (Tiers 1-3) | 25.860% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 6.250% | Coming soon | Coming soon |

## FAQ

### Is there enough evidence to pick between GPT-5.4 nano and Mellum2-12B-A2.5B-Thinking?

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

- [GPT-5.4 nano vs GPT-5.4](/compare/gpt-5-4-vs-gpt-5-4-nano)
- [Mellum2-12B-A2.5B-Thinking vs GPT-5.4](/compare/gpt-5-4-vs-mellum2-12b-a2-5b-thinking)
- [GPT-5.4 nano vs GPT-5.4 mini](/compare/gpt-5-4-mini-vs-gpt-5-4-nano)
- [Mellum2-12B-A2.5B-Thinking vs GPT-5.4 mini](/compare/gpt-5-4-mini-vs-mellum2-12b-a2-5b-thinking)

## Explore More

- [GPT-5.4 nano profile](/models/gpt-5-4-nano)
- [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)