Skip to main content
BenchLM
Advertise

Model comparison

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

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-Instruct 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-Instruct 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-Instruct.

Updated July 23, 2026
Shared results
2
Claude Opus 4.8 only
51
Mellum2-12B-A2.5B-Instruct 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-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 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-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 Opus 4.8 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 Opus 4.8 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 scores and score margins for Claude Opus 4.8 and Mellum2-12B-A2.5B-Instruct
CategoryClaude Opus 4.8ΔMellum2-12B-A2.5B-Instruct
KnowledgeClaude Opus 4.862.7Margin← 21.8Mellum2-12B-A2.5B-Instruct40.9
AgenticClaude Opus 4.880.3MarginNo overlapMellum2-12B-A2.5B-InstructNot measured
CodingClaude Opus 4.881.1MarginNo overlapMellum2-12B-A2.5B-InstructNot measured
MathClaude Opus 4.853.9MarginNo overlapMellum2-12B-A2.5B-InstructNot measured
MultimodalClaude Opus 4.877.0MarginNo overlapMellum2-12B-A2.5B-InstructNot measured
Inst. FollowingClaude Opus 4.8Not measuredMarginNo overlapMellum2-12B-A2.5B-Instruct75.8

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-Instruct

  1. GPQA

    Knowledge
    Source ↗
    A 93.6%B 40.9%
    Winner: Claude Opus 4.8Δ 52.7
    GPQA: Claude Opus 4.8 scored 93.6%; Mellum2-12B-A2.5B-Instruct scored 40.9%. 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-InstructComparison
Input / output priceUSD per 1M tokensClaude Opus 4.8$5 input / $25 outputMellum2-12B-A2.5B-InstructNot availableA complete price comparison is not available.
Generation speedtokens per secondClaude Opus 4.8Not availableMellum2-12B-A2.5B-InstructNot availableA complete speed comparison is not available.
First-answer latencyseconds to first tokenClaude Opus 4.8Not availableMellum2-12B-A2.5B-InstructNot availableA complete latency comparison is not available.
Context windowmaximum listed tokensClaude Opus 4.81MMellum2-12B-A2.5B-Instruct128KClaude Opus 4.8 lists the larger context window.

Benchmark Deep Dive

Agentic
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-InstructResult
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 —44.2%Not comparable
Coding
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-InstructResult
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-InstructResult
AA-LCRSource 67.7%—Not comparable
CritPtSource 20.9%—Not comparable
KnowledgeClaude Opus 4.8 wins
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-InstructResult
GPQASource 93.6%40.9%Claude Opus 4.8 leads
GPQA-DSource 93.6%40.9%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 —78.1%Not comparable
Math
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-InstructResult
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-InstructResult
INCLUDESource 87.6%—Not comparable
Multimodal
BenchmarkClaude Opus 4.8Mellum2-12B-A2.5B-InstructResult
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-InstructResult
AA-IFBenchSource 62.2%—Not comparable
IFEvalSource —75.8%Not comparable
Frequently Asked Questions (2)

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

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

Claude Opus 4.8 has the edge for knowledge tasks in this comparison, averaging 62.7 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.

Related Comparisons

Explore More

Anthropic Compare Pricing Methodology Find Your Best LLM Overall Rankings
Last updated: July 23, 2026

Choose a model with this week’s evidence

Join 2,000+ readers for ranking moves, pricing changes, and the claims that still need proof.

One email each week. Unsubscribe anytime.