Model comparison
GPT-5.5 Pro vs Mellum2-12B-A2.5B-Thinking
Head-to-head evidence from 0 shared benchmark results across 0 categories. Overall scores shown here use the public BenchAlign v5 ranking lane.
Public leaderboard positions: GPT-5.5 Pro #38 (Estimated); Mellum2-12B-A2.5B-Thinking unranked (Not scored). Intervals and evidence labels describe ranking uncertainty, not a guarantee for a specific workload.
Evidence parity. GPT-5.5 Pro and Mellum2-12B-A2.5B-Thinking share 0 comparable benchmark results. 1 of 8 categories are comparable. 7 results are unique to GPT-5.5 Pro; 5 to Mellum2-12B-A2.5B-Thinking.
Updated July 23, 2026- Shared results
- 0
- GPT-5.5 Pro only
- 7
- Mellum2-12B-A2.5B-Thinking only
- 5
- Comparable categories
- 1 / 8
Treat this as a split decision. GPT-5.5 Pro makes more sense if you need the larger 1M context window; Mellum2-12B-A2.5B-Thinking is the better fit if knowledge is the priority.
Confidence note. This is a partial-evidence comparison with 0 shared benchmark results across 0 evidence categories; 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-5.5 Pro and Mellum2-12B-A2.5B-Thinking 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-5.5 Pro gives you the larger context window at 1M, compared with 128K for Mellum2-12B-A2.5B-Thinking.
Operational comparison
Runtime and commercial metrics are compared only when both models have a complete sourced value.
| Metric | GPT-5.5 Pro | Mellum2-12B-A2.5B-Thinking | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | GPT-5.5 Pro$30 input / $180 output | Mellum2-12B-A2.5B-ThinkingNot available | A complete price comparison is not available. |
| Generation speedtokens per second | GPT-5.5 ProNot available | Mellum2-12B-A2.5B-ThinkingNot available | A complete speed comparison is not available. |
| First-answer latencyseconds to first token | GPT-5.5 ProNot available | Mellum2-12B-A2.5B-ThinkingNot available | A complete latency comparison is not available. |
| Context windowmaximum listed tokens | GPT-5.5 Pro1M | Mellum2-12B-A2.5B-Thinking128K | GPT-5.5 Pro lists the larger context window. |
Benchmark Deep Dive
Agentic2 benchmarks
Reasoning1 benchmarks
| Benchmark | GPT-5.5 Pro | Mellum2-12B-A2.5B-Thinking | Result |
|---|---|---|---|
| CritPtSource | 30.6% | — | Not comparable |
KnowledgeMellum2-12B-A2.5B-Thinking wins5 benchmarks
Math3 benchmarks
Inst. Following1 benchmarks
| Benchmark | GPT-5.5 Pro | Mellum2-12B-A2.5B-Thinking | Result |
|---|---|---|---|
| IFEvalSource | — | 76.5% | Not comparable |
Frequently Asked Questions (2)
Which is better, GPT-5.5 Pro or Mellum2-12B-A2.5B-Thinking?
GPT-5.5 Pro and Mellum2-12B-A2.5B-Thinking 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-5.5 Pro or Mellum2-12B-A2.5B-Thinking?
Mellum2-12B-A2.5B-Thinking has the edge for knowledge tasks in this comparison, averaging 57.6 versus 57.2. GPT-5.5 Pro stays close enough that the answer can still flip depending on your workload.
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