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Compare performance benchmarks, coding intelligence, reasoning evaluations, context limits, and API economics between Claude Opus 5.5 (Anthropic) and Step 5 Preview (StepFun).
| Metric / Capability | Claude Opus 5.5 | Step 5 Preview |
|---|---|---|
| Developer / Organization | Anthropic | StepFun |
| Release Date | 2026-09-22 | 2026-10-08 |
| Deployment / Weights | Proprietary Cloud API | Open Weights |
| Context Window | 1M tokens (1,000,000 tokens) | 1.0M tokens (1,048,576 tokens) |
| Input Pricing (/1M Tokens) | $4 | Free (Open Weights) |
| Output Pricing (/1M Tokens) | $20 | Free (Open Weights) |
| Benchmark / Domain | Claude Opus 5.5 | Step 5 Preview | Advantage |
|---|---|---|---|
Artificial Analysis Intelligence Index Composite index aggregating 10+ evaluations of general reasoning and knowledge. | 57.6% | 43.7% | Claude Opus 5.5 (+32%) |
Artificial Analysis Coding Agent Index v2.0 Composite index of coding-agent systems (model + harness) across FrontierCode v1.1, SWE-Atlas-QnA, and Terminal-Bench v4. | 61.7% | 43.1% | Claude Opus 5.5 (+43%) |
SWE-bench Pro Harder, contamination-resistant successor to SWE-bench spanning multiple languages. | 89.9% | — | — |
Terminal-Bench 4.0 Sandboxed command-line tasks requiring shell and file-system operation. | 66.4% | 33.3% | Claude Opus 5.5 (+99%) |
ARC-AGI-2 Novel visual grid puzzles requiring abstract rule induction. | 91.7% | — | — |
GPQA Diamond Graduate-level physics, chemistry, and biology questions written by domain experts. | — | 93.5% | — |
Humanity's Last Exam Expert-written questions across hundreds of disciplines designed to resist saturation. | 64.4% | 46.5% | Claude Opus 5.5 (+38%) |
FrontierMath v2 (Tiers 1-3) Unpublished, research-level mathematics problems across Tiers 1-3. | 91.2% | — | — |
Design Arena ELO Human-preference ELO across UI, 3D, data-visualization, and game-dev generations. | 1468 | — | — |
Claude Opus 5.5 leads across 4 evaluated benchmarks compared to 0 for Step 5 Preview, showing notable advantages in Artificial Analysis Intelligence Index, Artificial Analysis Coding Agent Index v2.0, Terminal-Bench 4.0.
Step 5 Preview has the larger context capacity of 1.0M tokens (1,048,576 tokens), compared to 1M tokens for Claude Opus 5.5.
Step 5 Preview is more economical. Input tokens cost $Free (Open Weights)/M tokens compared to $4/M tokens for Claude Opus 5.5.
Claude Opus 5.5 is a proprietary cloud API. Step 5 Preview is an open-weights model.
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