Claude Sonnet 4

Claude Sonnet 4 is a hybrid reasoning model designed to balance strong coding ability with efficient, everyday responsiveness, sitting in the Claude family as a practical workhorse between lighter tiers and the heavier Opus class. Its design intent centers on pairing a fast, capable non-thinking mode with an extended thinking mode that can interleave reasoning with tool use, parallel tool calls, and richer memory of local files. According to Anthropic's launch notes, it also introduces new capabilities around parallel tool orchestration and improved instruction following, which together make it well suited for both user-facing assistants and autonomous agent loops where precise control over behavior matters.

Sonnet 4 is presented as a clear generational upgrade over Claude Sonnet 3.7, sharpening coding and reasoning while remaining practical for high-volume deployment. The OpenRouter model page reports state-of-the-art SWE-bench performance at 72.7 percent, alongside improvements in autonomous codebase navigation, lower error rates in agent-driven workflows, and tighter adherence to complex instructions, all of which trace back to Anthropic's hybrid post-training approach that combines classic responses with extended thinking plus tool use. Anthropic highlights Sonnet 4 as ideal for coding workflows, user-facing assistants, and large-scale tasks where a balance of capability and efficiency matters, and its later integration into GitHub Copilot across paid plans underscores that practical developer focus. As the broader Sonnet lineage has continued to evolve through 4.5 and 4.6, Sonnet 4 stands as the foundational hybrid reasoning release that set the template for more capable and longer-context successors.