Claude Opus 5.5
Claude Opus 5.5 is Anthropic’s flagship frontier reasoning engine and the inaugurating model of the Claude 5.5 generation. Built specifically for long-horizon agentic coding, massive repository migrations, deep scientific research, and complex knowledge work, Opus 5.5 delivers high-tier performance while significantly reducing overall operational costs.
Model Overview
Opus 5.5 introduces an architectural shift toward highly efficient, multi-step task execution. It completes complex multi-file engineering tasks in fewer turns and using fewer tokens than its predecessors, delivering superior output while reducing total task orchestration costs.
- Developer: Anthropic
- Model Family: Claude 5.5
- Release Date: September 22, 2026
- Primary Target Use Cases: Autonomous multi-repository codebase refactoring, long-running agent loops, financial/legal modeling, dense document auditing, and verification-gated research.
Core Capabilities & Performance Profile
Accelerated Agentic Coding & Refactoring
- Higher Task Efficiency: Engineered to sustain autonomous agent execution over long sessions (such as hours-long audits or complex migrations) with minimal user intervention.
- Clear Execution Transparency: Communicates intermediate progress, findings, and needed inputs in plain language during turn-based agent execution.
- Reduced Token Footprint: Requires fewer total tokens and generation turns to complete complex, multi-file software tasks compared to earlier Opus versions.
Always-On Adaptive Thinking
- Embedded Reasoning: Adaptive thinking is enabled natively across all generation turns, allowing the model to dynamically determine the appropriate chain-of-thought depth per request.
- Effort-Based Control: Replaces manual thinking budgets with high-level effort settings (
low, medium, high, xhigh, max) to match logic depth against execution latency.
Technical Specifications
| Parameter |
Specification |
| Model Class |
Frontier Multimodal Reasoning Engine |
| Input Context Window |
1,000,000 tokens (1M) |
| Input Modalities |
Text, Code, Images (Vision), Structured PDFs |
| Output Modalities |
Text, Code, Structured JSON |
| Reasoning Engine |
Always-On Adaptive Thinking (effort: low, medium, high, xhigh, max) |
| Native Tools |
Computer / Browser Use, Function Calling, Code Execution, Vision Parsing |
Safety & Specialized Verification Programs
Claude Opus 5.5 incorporates Anthropic’s updated safety classifiers for high-risk domain evaluation:
- Domain Safety Classifiers: Uses refined classification layers similar to Claude Fable 5.1 in biology, cybersecurity, and advanced AI research to enforce strict safety boundaries.
- Life Sciences Verification Program: Unlocks unrestricted biology and pathodynamics research capabilities for verified academic and research institutions.
- Cyber Verification Program: Dedicated access program for verified security practitioners performing vulnerability research and patch generation.
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