Anthropic claims that Claude Sonnet 4.5 is the best code model in the world. It also comes with significant improvements in reasoning and mathematical skills. On OSWorld, a benchmark for AI models that perform real-world computing tasks, Sonnet 4.5 leads with 61.4 percent. Four months ago, Sonnet 4 scored 42.2 percent on this test. Along with the model, Anthropics is also introducing the Claude Agent SDK.