Claude Sonnet 4.5 (September 29, 2025 version) is Anthropic's powerful and versatile hybrid reasoning model, supporting extended thinking chain and interleaved tool use. It leads globally in coding, agent tasks, and computer operations, supports a 200K token context window (approximately 150K English words, 1M preview version), integrates visual reasoning, memory tools, and context editing features, and is suitable for long-duration autonomous work such as software development, multi-agent systems, and financial analysis. Compared to Sonnet 4, it shows significant improvements on SWE-bench Verified (77.2%) and GPQA Diamond (83.4%) benchmarks, balances speed and cost, is the top choice for developer agents and enterprise productivity, and offers the best safety alignment (reducing deception and sycophancy behaviors).