Claude Sonnet 4.5 is Anthropic's most advanced Sonnet model prior to the 4.6 generation, optimized for real-world agents and coding workflows. It delivers state-of-the-art coding performance with improvements in system design, code security, and specification adherence. The model is designed for extended autonomous operation with fact-based progress tracking, and introduces stronger agentic capabilities including speculative parallel execution, improved tool orchestration, and efficient context and memory management for multi-context, long-running workflows.