Claude Sonnet 4.5

Overview

Claude Sonnet 4.5 represents Anthropic's most advanced AI model, combining exceptional intelligence with industry-leading capabilities in coding and complex reasoning. Released in 2025, the model achieves a groundbreaking 61.4% score on the OSWorld benchmark, which measures performance on real-world computer tasks including browsing, coding, and application use. This makes Claude Sonnet 4.5 the best model for practical computer-based work and software development.

A distinctive feature of Claude Sonnet 4.5 is its extended thinking capability, which allows the model to engage in deep, focused reasoning for 30+ hours on complex problems. Combined with a 500K token context window, exceptional coding abilities, and Constitutional AI safety training, Claude Sonnet 4.5 delivers powerful performance while maintaining high standards for helpfulness, harmlessness, and honesty. The model excels at long-form analysis, complex software development, and nuanced problem-solving that requires sustained concentration.

Key Features

• 61.4% performance on OSWorld benchmark (industry-leading computer task capability)
• Extended thinking mode supporting 30+ hours of focused reasoning
• 500K token context window for processing entire codebases and extensive documents
• Best-in-class coding capabilities across multiple programming languages
• Superior reasoning and analytical thinking for complex problems
• Constitutional AI training for enhanced safety and alignment
• Exceptional instruction following and task completion accuracy
• Strong performance in mathematical and scientific domains
• Nuanced understanding of complex, multi-layered instructions
• Extended conversation memory with remarkable coherence
• Vision capabilities for image analysis and understanding
• Reduced refusals on legitimate requests with improved helpfulness

Use Cases

• Advanced software development and architectural design
• Complex code review and security analysis
• Long-form research and academic writing
• Technical documentation and API design
• Scientific paper analysis and literature review
• Business strategy development and decision support
• Legal document analysis and contract review
• Data analysis with extended reasoning requirements
• Educational content development and curriculum design
• Creative writing projects requiring deep narrative coherence
• Multi-step problem solving in specialized domains

Technical Specifications

Claude Sonnet 4.5 utilizes a transformer-based architecture optimized for both performance and safety. The model supports text and image inputs with text outputs, featuring advanced tokenization and efficient processing of long contexts. It's accessible through REST API, Python SDK, and TypeScript SDK with comprehensive documentation. The extended thinking mode operates as a separate capability that can be activated for problems requiring sustained deep reasoning.

Extended Thinking Capabilities

Claude Sonnet 4.5's extended thinking feature enables the model to work on complex problems with sustained focus for 30+ hours. This capability is particularly valuable for intricate coding projects, complex mathematical proofs, detailed research analysis, and any task requiring deep, prolonged concentration. The model maintains context and reasoning chains throughout the extended session, producing highly coherent and well-reasoned outputs.

OSWorld Benchmark Leadership

Claude Sonnet 4.5's 61.4% score on the OSWorld benchmark represents the highest performance among all AI models on practical computer tasks. OSWorld measures the ability to perform real-world tasks like using web browsers, writing and debugging code, using desktop applications, and navigating complex interfaces. This exceptional performance makes Claude Sonnet 4.5 particularly effective for software development, research, and knowledge work.

Safety and Alignment

Built using Constitutional AI methodology, Claude Sonnet 4.5 incorporates extensive safety training and alignment techniques. The model is designed to be helpful, honest, and harmless, with sophisticated mechanisms to avoid generating harmful content while remaining maximally useful for legitimate applications. Anthropic's approach balances capability with responsibility, ensuring the model can tackle complex tasks while maintaining ethical boundaries.

Pricing and Availability

Claude Sonnet 4.5 is available through Anthropic's API with competitive pricing based on input and output tokens. Extended thinking mode has separate pricing due to its computational requirements. Enterprise plans offer volume discounts, dedicated support, and SLA guarantees. The model is also available through AWS Bedrock and Google Cloud Vertex AI for integrated cloud deployments.