Anthropic: claude-opus-4.1:free

Claude Opus 4.1 is a targeted performance upgrade to Anthropic's flagship Opus 4 series. Serving as a drop-in replacement, it maintains the same API footprint and pricing while delivering substantial gains in real-world software engineering and long-horizon agentic workflows. Scoring 74.5% on SWE-bench Verified, it outperforms the original Opus 4 by providing superior multi-file refactoring and pinpoint error-tracking capabilities. It features a "hybrid reasoning" architecture that allows developers to toggle between near-instant responses and deep "Extended Thinking" modes. This makes it an industry leader for autonomous coding agents, enterprise-level knowledge assistants, and complex research-level synthesis.