Claude 4.5 Sonnet

Claude 4.5 Sonnet API Overview

Claude Sonnet 4.5 by Anthropic is currently one of the most advanced AI models with a focus on software coding, complex agent tasks, and extended autonomous computer use. It excels in long-term multi-step tasks with strong reasoning, domain knowledge, and computer interaction capabilities. Sonnet 4.5 is designed to deliver superior accuracy, reliability, and safety in demanding real-world environments such as finance, cybersecurity, research, and development workflows.

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Technical Specifications

• Primary Strengths: Software engineering, complex agents, computer usage automation
• SWE-bench Verified: 77.2% accuracy (with extended thinking mode enabled)
• OSWorld benchmark: 61.4% for real-world computer task completion‍
• Extended Thinking Mode: Improves performance on complex reasoning, multi-step coding, and agentic workflows by enabling deeper thought processes at some cost to latency and caching efficiency‍
• Context Management: Exceptional long-term state tracking via advanced context window and external file state awareness; effective memory for maintaining focus over sessions spanning hours

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Performance Benchmarks

Sonnet 4.5 incorporates advanced long-term context management, enabling it to maintain awareness and focus over sessions lasting hours, which is crucial for coding projects, multi-agent coordination, and extended computer interactions. Its enhanced tool usage capabilities allow the model to control multiple processes in parallel, improving efficiency in autonomous workflows such as complex software debugging, data synthesis, and financial or cybersecurity analysis. This model stands out due to its hybrid architecture that supports both fast reasoning and an extended thinking mode for deep problem-solving.

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Key Features

• Best Coding Model to Date: Achieves state-of-the-art performance on coding benchmarks like SWE-bench Verified with 77.2% accuracy, excels throughout the software development lifecycle including planning, system design, and debugging.
• Extended Autonomous Operation: Capable of working independently for over 30 hours on complex, multi-step tasks while maintaining clarity and incremental progress updates, making it reliable for long-running workflows.
• Hybrid Reasoning Architecture: Supports an extended thinking mode that boosts performance on complex coding and reasoning tasks, balanced with a standard fast reasoning mode.‍
• Improved Safety & Security: Integrates robust security engineering and vulnerability detection, reducing risks in sensitive coding and financial applications.‍
• Broad Domain Knowledge: Significant improvements in domain-specific reasoning, including finance, cybersecurity, medicine, and STEM fields, supporting sophisticated real-world applications.

Claude 4.5 Sonnet API Pricing

• Base Input Tokens: $3.15 per million tokens‍
• 5m Cache Writes: $3.9375 per million tokens‍
• 1h Cache Writes: $6.3 per million tokens‍
• Cache Hits & Refreshes: $0.315 per million tokens‍
• Output Tokens: $15.75 per million tokens

Use Cases

• Programming assistance: writing, debugging, and reviewing multi-step complex code over extended sessions
• Autonomous agents: managing workflows that coordinate multiple software tools and data sources
• Financial analysis agents: parsing and analyzing large datasets with domain-specific expertise
• Cybersecurity automation: vulnerability detection and threat response scripting
• Research assistance: multi-agent coordination for data synthesis and summarization

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Code Sample

Comparison to Other Models

vs GPT-5: Claude Sonnet 4.5 is currently regarded as the best coding model in practice, often outperforming GPT-5 Codex in live coding tests and benchmarks. It excels in complex multi-step coding tasks with a balance of speed and accuracy, although GPT-5 holds a slight edge in some high-level reasoning cases. Sonnet 4.5 is priced higher than GPT-5 but delivers strong reliability and safety.

vs Qwen3-Next-80B: Sonnet 4.5 surpasses Qwen3-Next-80B in real-world coding and autonomous agent benchmarks, with better accuracy and deeper reasoning capabilities. Qwen3 is more efficiency-optimized for throughput but lacks the advanced multi-agent support and domain specialization seen in Claude Sonnet 4.5. Sonnet also demonstrates superior safety and context window size.

vs Gemini 2.5 Pro: Claude Sonnet 4.5 outperforms Gemini 2.5 Pro significantly on coding benchmarks, achieving 77.2% accuracy on SWE-bench compared to Gemini's 63.8%. It also supports longer autonomous operation (30+ hours) and better multitasking in agentic scenarios, making it the preferred choice for complex software engineering and AI agent workflows.

vs Opus 4.1: Sonnet 4.5 shows substantial improvements over Anthropic's previous Opus 4.1 with nearly a 20% jump in real-world AI computer use tasks and better coding precision. The newer model integrates advanced multi-agent tool usage and offers extended context windows, enhancing both accuracy and sustained task execution.

API Integration

Accessible via AI/ML API. Documentation: available here.

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