Model comparison
Claude Mythos 5 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: Claude Mythos 5 #1 (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. Claude Mythos 5 and Mellum2-12B-A2.5B-Instruct share 1 comparable benchmark result. 1 of 8 categories are comparable. 14 results are unique to Claude Mythos 5; 4 to Mellum2-12B-A2.5B-Instruct.
Updated July 23, 2026- Shared results
- 1
- Claude Mythos 5 only
- 14
- Mellum2-12B-A2.5B-Instruct only
- 4
- Comparable categories
- 1 / 8
Treat this as a split decision. Claude Mythos 5 makes more sense if knowledge is the priority or you need the larger 1M+ 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
Claude Mythos 5 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.
Claude Mythos 5 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. Claude Mythos 5 gives you the larger context window at 1M+, 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 | Claude Mythos 5 | Δ | Mellum2-12B-A2.5B-Instruct |
|---|---|---|---|
| Knowledge | Claude Mythos 568.5 | Margin← 27.6 | Mellum2-12B-A2.5B-Instruct40.9 |
| Agentic | Claude Mythos 587.0 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Coding | Claude Mythos 589.7 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Math | Claude Mythos 597.6 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Multimodal | Claude Mythos 593.5 | MarginNo overlap | Mellum2-12B-A2.5B-InstructNot measured |
| Inst. Following | Claude Mythos 5Not 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 94.1%B 40.9%Winner: Claude Mythos 5Δ 53.2GPQA: Claude Mythos 5 scored 94.1%; Mellum2-12B-A2.5B-Instruct scored 40.9%. Claude Mythos 5 wins this benchmark.
Operational comparison
Runtime and commercial metrics are compared only when both models have a complete sourced value.
| Metric | Claude Mythos 5 | Mellum2-12B-A2.5B-Instruct | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | Claude Mythos 5$10 input / $50 output | Mellum2-12B-A2.5B-InstructNot available | A complete price comparison is not available. |
| Generation speedtokens per second | Claude Mythos 5Not available | Mellum2-12B-A2.5B-InstructNot available | A complete speed comparison is not available. |
| First-answer latencyseconds to first token | Claude Mythos 5Not available | Mellum2-12B-A2.5B-InstructNot available | A complete latency comparison is not available. |
| Context windowmaximum listed tokens | Claude Mythos 51M+ | Mellum2-12B-A2.5B-Instruct128K | Claude Mythos 5 lists the larger context window. |
Benchmark Deep Dive
Agentic5 benchmarks
Coding3 benchmarks
KnowledgeClaude Mythos 5 wins5 benchmarks
Math1 benchmarks
| Benchmark | Claude Mythos 5 | Mellum2-12B-A2.5B-Instruct | Result |
|---|---|---|---|
| USAMO 2026Source | 97.6% | — | Not comparable |
Multilingual1 benchmarks
| Benchmark | Claude Mythos 5 | Mellum2-12B-A2.5B-Instruct | Result |
|---|---|---|---|
| SWE MultilingualSource | 92.2% | — | Not comparable |
Multimodal3 benchmarks
Inst. Following1 benchmarks
| Benchmark | Claude Mythos 5 | Mellum2-12B-A2.5B-Instruct | Result |
|---|---|---|---|
| IFEvalSource | — | 75.8% | Not comparable |
Frequently Asked Questions (2)
Which is better, Claude Mythos 5 or Mellum2-12B-A2.5B-Instruct?
Claude Mythos 5 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, Claude Mythos 5 or Mellum2-12B-A2.5B-Instruct?
Claude Mythos 5 has the edge for knowledge tasks in this comparison, averaging 68.5 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
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