Model comparison
Mellum2-12B-A2.5B-Instruct vs o3-mini
Head-to-head evidence from 2 shared benchmark results across 2 categories. Overall scores shown here use the public BenchAlign v5 ranking lane.
Public leaderboard positions: Mellum2-12B-A2.5B-Instruct unranked (Not scored); o3-mini #136 (Supported). Intervals and evidence labels describe ranking uncertainty, not a guarantee for a specific workload.
Evidence parity. Mellum2-12B-A2.5B-Instruct and o3-mini share 2 comparable benchmark results. 2 of 8 categories are comparable. 3 results are unique to Mellum2-12B-A2.5B-Instruct; 8 to o3-mini.
Updated July 23, 2026- Shared results
- 2
- Mellum2-12B-A2.5B-Instruct only
- 3
- o3-mini only
- 8
- Comparable categories
- 2 / 8
Treat this as a split decision. Mellum2-12B-A2.5B-Instruct makes more sense if you would rather avoid the extra latency and token burn of a reasoning model; o3-mini is the better fit if knowledge is the priority or you need the larger 200K context window.
Confidence note. This is a partial-evidence comparison with 2 shared benchmark results across 2 evidence categories; 2 of 8 categories currently have scoreable aggregates for both models. Treat the verdict as directional until coverage is more balanced.
Why this result
Mellum2-12B-A2.5B-Instruct and o3-mini 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.
o3-mini 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. o3-mini gives you the larger context window at 200K, 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 | Mellum2-12B-A2.5B-Instruct | Δ | o3-mini |
|---|---|---|---|
| Knowledge | Mellum2-12B-A2.5B-Instruct40.9 | Margin→ 36.3 | o3-mini77.2 |
| Inst. Following | Mellum2-12B-A2.5B-Instruct75.8 | Margin→ 18.1 | o3-mini93.9 |
| Coding | Mellum2-12B-A2.5B-InstructNot measured | MarginNo overlap | o3-mini49.3 |
Decisive benchmark drivers
The largest measured benchmark gaps in this matchup, with exact reported values.
More
- Source ↗
GPQA
KnowledgeA 40.9%B 77.2%Winner: o3-miniΔ 36.3GPQA: Mellum2-12B-A2.5B-Instruct scored 40.9%; o3-mini scored 77.2%. o3-mini wins this benchmark. - Source ↗
IFEval
Inst. FollowingA 75.8%B 93.9%Winner: o3-miniΔ 18.1IFEval: Mellum2-12B-A2.5B-Instruct scored 75.8%; o3-mini scored 93.9%. o3-mini wins this benchmark.
Operational comparison
Runtime and commercial metrics are compared only when both models have a complete sourced value.
| Metric | Mellum2-12B-A2.5B-Instruct | o3-mini | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | Mellum2-12B-A2.5B-InstructNot available | o3-mini$1.1 input / $4.4 output | A complete price comparison is not available. |
| Generation speedtokens per second | Mellum2-12B-A2.5B-InstructNot available | o3-mini160 tok/s | A complete speed comparison is not available. |
| First-answer latencyseconds to first token | Mellum2-12B-A2.5B-InstructNot available | o3-mini7.12 s | A complete latency comparison is not available. |
| Context windowmaximum listed tokens | Mellum2-12B-A2.5B-Instruct128K | o3-mini200K | o3-mini lists the larger context window. |
Benchmark Deep Dive
Agentic2 benchmarks
Coding2 benchmarks
Knowledgeo3-mini wins7 benchmarks
| Benchmark | Mellum2-12B-A2.5B-Instruct | o3-mini | Result |
|---|---|---|---|
| MMLU-ReduxSource | 78.1% | — | Not comparable |
| GPQASource | 40.9% | 77.2% | o3-mini leads |
| GPQA-DSource | 40.9% | — | Not comparable |
| MMLUSource | — | 86.9% | Not comparable |
| Artificial Analysis Intelligence IndexSource | — | 19.0% | Not comparable |
| AA-GPQA DiamondSource | — | 74.8% | Not comparable |
| AA-HLESource | — | 8.7% | Not comparable |
Math1 benchmarks
| Benchmark | Mellum2-12B-A2.5B-Instruct | o3-mini | Result |
|---|---|---|---|
| AIME 2024Source | — | 87.3% | Not comparable |
Inst. Followingo3-mini wins1 benchmarks
| Benchmark | Mellum2-12B-A2.5B-Instruct | o3-mini | Result |
|---|---|---|---|
| IFEvalSource | 75.8% | 93.9% | o3-mini leads |
Frequently Asked Questions (3)
Which is better, Mellum2-12B-A2.5B-Instruct or o3-mini?
Mellum2-12B-A2.5B-Instruct and o3-mini 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, Mellum2-12B-A2.5B-Instruct or o3-mini?
o3-mini has the edge for knowledge tasks in this comparison, averaging 77.2 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
Which is better for instruction following, Mellum2-12B-A2.5B-Instruct or o3-mini?
o3-mini has the edge for instruction following in this comparison, averaging 93.9 versus 75.8. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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