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Model comparison

Claude Opus 4.8 vs Mellum2-12B-A2.5B-Thinking

Data verified

Head-to-head evidence from 2 shared benchmark results across 1 category. Overall scores shown here use the public BenchAlign v5 ranking lane.

78.34/100
No comparison
N/A
1 category wins0 category wins

Public leaderboard positions: Claude Opus 4.8 #5 (Supported); Mellum2-12B-A2.5B-Thinking unranked (Not scored). Intervals and evidence labels describe ranking uncertainty, not a guarantee for a specific workload.

Evidence parity. Claude Opus 4.8 and Mellum2-12B-A2.5B-Thinking share 2 comparable benchmark results. 1 of 8 categories are comparable. 51 results are unique to Claude Opus 4.8; 3 to Mellum2-12B-A2.5B-Thinking.

Updated July 23, 2026
Shared results
2
Claude Opus 4.8 only
51
Mellum2-12B-A2.5B-Thinking only
3
Comparable categories
1 / 8

Treat this as a split decision. Claude Opus 4.8 makes more sense if knowledge is the priority or you need the larger 1M context window; Mellum2-12B-A2.5B-Thinking is the better fit if its strengths line up with your actual workload.

Confidence note. This is a partial-evidence comparison with 2 shared benchmark results 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 Opus 4.8 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.

Claude Opus 4.8 gives you the larger context window at 1M, 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 scores and score margins for Claude Opus 4.8 and Mellum2-12B-A2.5B-Thinking
CategoryClaude Opus 4.8ΔMellum2-12B-A2.5B-Thinking
KnowledgeClaude Opus 4.862.7Margin← 5.1Mellum2-12B-A2.5B-Thinking57.6
AgenticClaude Opus 4.880.3MarginNo overlapMellum2-12B-A2.5B-ThinkingNot measured
CodingClaude Opus 4.881.1MarginNo overlapMellum2-12B-A2.5B-ThinkingNot measured
MathClaude Opus 4.853.9MarginNo overlapMellum2-12B-A2.5B-ThinkingNot measured
MultimodalClaude Opus 4.877.0MarginNo overlapMellum2-12B-A2.5B-ThinkingNot measured
Inst. FollowingClaude Opus 4.8Not measuredMarginNo overlapMellum2-12B-A2.5B-Thinking76.5

Decisive benchmark drivers

The largest measured benchmark gaps in this matchup, with exact reported values.

More
A · Claude Opus 4.8B · Mellum2-12B-A2.5B-Thinking

  1. GPQA

    Knowledge
    Source ↗
    A 93.6%B 57.6%
    Winner: Claude Opus 4.8Δ 36
    GPQA: Claude Opus 4.8 scored 93.6%; Mellum2-12B-A2.5B-Thinking scored 57.6%. Claude Opus 4.8 wins this benchmark.

Operational comparison

Runtime and commercial metrics are compared only when both models have a complete sourced value.

MetricClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingComparison
Input / output priceUSD per 1M tokensClaude Opus 4.8$5 input / $25 outputMellum2-12B-A2.5B-ThinkingNot availableA complete price comparison is not available.
Generation speedtokens per secondClaude Opus 4.8Not availableMellum2-12B-A2.5B-ThinkingNot availableA complete speed comparison is not available.
First-answer latencyseconds to first tokenClaude Opus 4.8Not availableMellum2-12B-A2.5B-ThinkingNot availableA complete latency comparison is not available.
Context windowmaximum listed tokensClaude Opus 4.81MMellum2-12B-A2.5B-Thinking128KClaude Opus 4.8 lists the larger context window.

Benchmark Deep Dive

Agentic
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
Terminal-Bench 2.0Source 74.6%—Not comparable
BrowseCompSource 84.3%—Not comparable
DeepSearchQASource 93.1%—Not comparable
OSWorld-VerifiedSource 83.4%—Not comparable
Finance Agent v2Source 53.9%—Not comparable
GDPval-AASource 1594—Not comparable
MCP AtlasSource 82.2%—Not comparable
ToolathlonSource 59.9%—Not comparable
Gert LabsSource 72.97%—Not comparable
AA Agentic IndexSource 47.2%—Not comparable
τ²-bench resultsSource 94.4%—Not comparable
GDPval-AASource 54.7%—Not comparable
ResearchClawBenchSource 21.1%—Not comparable
OSWorld 2.0Source 20.6%—Not comparable
AA BriefcaseSource 1347—Not comparable
AA AutomationBenchSource 48.5%—Not comparable
AA EnterpriseOps-GymSource 44.0%—Not comparable
AA Harvey LABSource 91.1%—Not comparable
AA Tau3 BankingSource 27.6%—Not comparable
terminalBenchHardSource 58.3%—Not comparable
aaTerminalBench21Source 84.6%—Not comparable
BFCL v4Source —45.6%Not comparable
Coding
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
SWE-bench VerifiedSource 88.6%—Not comparable
SWE-bench ProSource 69.2%—Not comparable
SWE MultilingualSource 84.4%—Not comparable
SWE MultimodalSource 38.4%—Not comparable
Terminal-Bench 2.0Source 74.6%—Not comparable
cursorBench31Source 58.4%—Not comparable
cursorBench32Source 62.3%—Not comparable
AA Coding IndexSource 74.3%—Not comparable
AA-SciCodeSource 53.5%—Not comparable
FrontierCode 1.1 MainSource 46.5%—Not comparable
Reasoning
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
AA-LCRSource 67.7%—Not comparable
CritPtSource 20.9%—Not comparable
KnowledgeClaude Opus 4.8 wins
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
GPQASource 93.6%57.6%Claude Opus 4.8 leads
GPQA-DSource 93.6%57.6%Claude Opus 4.8 leads
HLESource 57.9%—Not comparable
HLE w/o toolsSource 49.8%—Not comparable
Artificial Analysis Intelligence IndexSource 55.7%—Not comparable
AA-GPQA DiamondSource 92.0%—Not comparable
AA-HLESource 45.7%—Not comparable
AA-Omniscience IndexSource 27.4%—Not comparable
AA-Omniscience AccuracySource 46.6%—Not comparable
AA-Omniscience Hallucination RateSource 35.9%—Not comparable
MMLU-ReduxSource —86.2%Not comparable
Math
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
USAMO 2026Source 96.7%—Not comparable
FrontierMath v2 (Tiers 1-3)Source 47.241%—Not comparable
FrontierMath v2 (Tier 4)Source 31.250%—Not comparable
Multilingual
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
INCLUDESource 87.6%—Not comparable
Multimodal
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
OfficeQA ProSource 66.2%—Not comparable
ScreenSpot ProSource 87.9%—Not comparable
CharXivSource 89.9%—Not comparable
CharXiv w/o toolsSource 80.5%—Not comparable
Design Arena WebsiteSource 1270—Not comparable
Inst. Following
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-ThinkingResult
AA-IFBenchSource 62.2%—Not comparable
IFEvalSource —76.5%Not comparable
Frequently Asked Questions (2)

Which is better, Claude Opus 4.8 or Mellum2-12B-A2.5B-Thinking?

Claude Opus 4.8 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, Claude Opus 4.8 or Mellum2-12B-A2.5B-Thinking?

Claude Opus 4.8 has the edge for knowledge tasks in this comparison, averaging 62.7 versus 57.6. Inside this category, GPQA is the benchmark that creates the most daylight between them.

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