Model comparison
Mellum2-12B-A2.5B-Thinking 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-Thinking 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-Thinking and o3-mini share 2 comparable benchmark results. 2 of 8 categories are comparable. 3 results are unique to Mellum2-12B-A2.5B-Thinking; 8 to o3-mini.
Updated July 23, 2026- Shared results
- 2
- Mellum2-12B-A2.5B-Thinking only
- 3
- o3-mini only
- 8
- Comparable categories
- 2 / 8
Treat this as a split decision. Mellum2-12B-A2.5B-Thinking makes more sense if its workflow fits your team better; 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-Thinking 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 gives you the larger context window at 200K, compared with 128K for Mellum2-12B-A2.5B-Thinking.
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-Thinking | Δ | o3-mini |
|---|---|---|---|
| Knowledge | Mellum2-12B-A2.5B-Thinking57.6 | Margin→ 19.6 | o3-mini77.2 |
| Inst. Following | Mellum2-12B-A2.5B-Thinking76.5 | Margin→ 17.4 | o3-mini93.9 |
| Coding | Mellum2-12B-A2.5B-ThinkingNot 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 57.6%B 77.2%Winner: o3-miniΔ 19.6GPQA: Mellum2-12B-A2.5B-Thinking scored 57.6%; o3-mini scored 77.2%. o3-mini wins this benchmark. - Source ↗
IFEval
Inst. FollowingA 76.5%B 93.9%Winner: o3-miniΔ 17.4IFEval: Mellum2-12B-A2.5B-Thinking scored 76.5%; 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-Thinking | o3-mini | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | Mellum2-12B-A2.5B-ThinkingNot available | o3-mini$1.1 input / $4.4 output | A complete price comparison is not available. |
| Generation speedtokens per second | Mellum2-12B-A2.5B-ThinkingNot available | o3-mini160 tok/s | A complete speed comparison is not available. |
| First-answer latencyseconds to first token | Mellum2-12B-A2.5B-ThinkingNot available | o3-mini7.12 s | A complete latency comparison is not available. |
| Context windowmaximum listed tokens | Mellum2-12B-A2.5B-Thinking128K | 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-Thinking | o3-mini | Result |
|---|---|---|---|
| MMLU-ReduxSource | 86.2% | — | Not comparable |
| GPQASource | 57.6% | 77.2% | o3-mini leads |
| GPQA-DSource | 57.6% | — | 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-Thinking | o3-mini | Result |
|---|---|---|---|
| AIME 2024Source | — | 87.3% | Not comparable |
Inst. Followingo3-mini wins1 benchmarks
| Benchmark | Mellum2-12B-A2.5B-Thinking | o3-mini | Result |
|---|---|---|---|
| IFEvalSource | 76.5% | 93.9% | o3-mini leads |
Frequently Asked Questions (3)
Which is better, Mellum2-12B-A2.5B-Thinking or o3-mini?
Mellum2-12B-A2.5B-Thinking 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-Thinking or o3-mini?
o3-mini has the edge for knowledge tasks in this comparison, averaging 77.2 versus 57.6. Inside this category, GPQA is the benchmark that creates the most daylight between them.
Which is better for instruction following, Mellum2-12B-A2.5B-Thinking or o3-mini?
o3-mini has the edge for instruction following in this comparison, averaging 93.9 versus 76.5. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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