Anthropic has launched Claude Sonnet 5, describing it as its most agentic Sonnet model yet. It is capable of autonomous planning, tool use, and verifying its own output without being prompted, Anthropic said. The model nears Opus 4.8-level performance on several benchmarks while costing significantly less. It also recorded lower hallucination and sycophancy rates than its predecessor, Sonnet 4.6.