Model comparison
GPT-5.4 nano vs Mellum2-12B-A2.5B-Instruct
Head-to-head evidence from 1 shared benchmark result across 1 category. Overall scores shown here use the public BenchAlign v5 ranking lane.
Public leaderboard positions: GPT-5.4 nano #25 (Supported); Mellum2-12B-A2.5B-Instruct unranked (Not scored). Intervals and evidence labels describe ranking uncertainty, not a guarantee for a specific workload.
Evidence parity. GPT-5.4 nano and Mellum2-12B-A2.5B-Instruct share 1 comparable benchmark result. 1 of 8 categories are comparable. 28 results are unique to GPT-5.4 nano; 4 to Mellum2-12B-A2.5B-Instruct.
Updated July 23, 2026- Shared results
- 1
- GPT-5.4 nano only
- 28
- Mellum2-12B-A2.5B-Instruct only
- 4
- Comparable categories
- 1 / 8
Treat this as a split decision. GPT-5.4 nano makes more sense if knowledge is the priority or you need the larger 400K context window; Mellum2-12B-A2.5B-Instruct is the better fit if you would rather avoid the extra latency and token burn of a reasoning model.
Confidence note. This is a partial-evidence comparison with 1 shared benchmark result across 1 evidence category; 1 of 8 categories currently have scoreable aggregates for both models. Treat the verdict as directional until coverage is more balanced.
Why this result
GPT-5.4 nano and Mellum2-12B-A2.5B-Instruct finish on the same BenchAlign overall score, so this is less about a single winner and more about where the edge shows up. The BenchAlign headline says tie; the benchmark table is where the real choice happens.
GPT-5.4 nano is the reasoning model in the pair, while Mellum2-12B-A2.5B-Instruct is not. That usually helps on harder chain-of-thought-heavy tests, but it can also mean more latency and more token spend in real use. GPT-5.4 nano gives you the larger context window at 400K, compared with 128K for Mellum2-12B-A2.5B-Instruct.
Category breakdown
Exact category averages are shown below. Not measured means BenchLM does not have enough sourced public coverage for that model and category.
| Category | GPT-5.4 nano | Δ | Mellum2-12B-A2.5B-Instruct |
|---|---|---|---|
| Knowledge | GPT-5.4 nano43.8 | Margin← 2.9 | Mellum2-12B-A2.5B-Instruct40.9 |
| Agentic | GPT-5.4 nano42.9 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Math | GPT-5.4 nano21.0 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Multimodal | GPT-5.4 nano66.1 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Inst. Following | GPT-5.4 nanoNot measured | MarginNo overlap | Mellum2-12B-A2.5B-Instruct75.8 |
Decisive benchmark drivers
The largest measured benchmark gaps in this matchup, with exact reported values.
More
- Source ↗
GPQA
KnowledgeA 82.8%B 40.9%Winner: GPT-5.4 nanoΔ 41.9GPQA: GPT-5.4 nano scored 82.8%; Mellum2-12B-A2.5B-Instruct scored 40.9%. GPT-5.4 nano wins this benchmark.
Operational comparison
Runtime and commercial metrics are compared only when both models have a complete sourced value.
| Metric | GPT-5.4 nano | Mellum2-12B-A2.5B-Instruct | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | GPT-5.4 nano$0.2 input / $1.25 output | Mellum2-12B-A2.5B-InstructNot available | A complete price comparison is not available. |
| Generation speedtokens per second | GPT-5.4 nano191 tok/s | Mellum2-12B-A2.5B-InstructNot available | A complete speed comparison is not available. |
| First-answer latencyseconds to first token | GPT-5.4 nano3.64 s | Mellum2-12B-A2.5B-InstructNot available | A complete latency comparison is not available. |
| Context windowmaximum listed tokens | GPT-5.4 nano400K | Mellum2-12B-A2.5B-Instruct128K | GPT-5.4 nano lists the larger context window. |
Benchmark Deep Dive
Agentic10 benchmarks
| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Instruct | Result |
|---|---|---|---|
| Terminal-Bench 2.0Source | 46.3% | — | Not comparable |
| OSWorld-VerifiedSource | 39% | — | Not comparable |
| MCP AtlasSource | 56.1% | — | Not comparable |
| ToolathlonSource | 35.5% | — | Not comparable |
| τ²-bench resultsSource | 76% | — | Not comparable |
| AA Agentic IndexSource | 27.5% | — | Not comparable |
| APEX-Agents-AASource | 24.9% | — | Not comparable |
| GDPval-AASource | 30.0% | — | Not comparable |
| GDPval-AASource | 1100 | — | Not comparable |
| BFCL v4Source | — | 44.2% | Not comparable |
Coding3 benchmarks
Reasoning2 benchmarks
KnowledgeGPT-5.4 nano wins11 benchmarks
| Benchmark | GPT-5.4 nano | Mellum2-12B-A2.5B-Instruct | Result |
|---|---|---|---|
| GPQASource | 82.8% | 40.9% | GPT-5.4 nano leads |
| HLESource | 37.7% | — | Not comparable |
| HLE w/o toolsSource | 24.3% | — | Not comparable |
| Artificial Analysis Intelligence IndexSource | 38.2% | — | Not comparable |
| AA-GPQA DiamondSource | 81.7% | — | Not comparable |
| AA-HLESource | 26.5% | — | Not comparable |
| AA-Omniscience IndexSource | -29.5% | — | Not comparable |
| AA-Omniscience AccuracySource | 25.4% | — | Not comparable |
| AA-Omniscience Hallucination RateSource | 73.6% | — | Not comparable |
| MMLU-ReduxSource | — | 78.1% | Not comparable |
| GPQA-DSource | — | 40.9% | Not comparable |
Math2 benchmarks
Multimodal3 benchmarks
Frequently Asked Questions (2)
Which is better, GPT-5.4 nano or Mellum2-12B-A2.5B-Instruct?
GPT-5.4 nano and Mellum2-12B-A2.5B-Instruct are tied on the BenchAlign overall score, so the right pick depends on which category matters most for your use case.
Which is better for knowledge tasks, GPT-5.4 nano or Mellum2-12B-A2.5B-Instruct?
GPT-5.4 nano has the edge for knowledge tasks in this comparison, averaging 43.8 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
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