Claude Opus 4 arrived May 22, 2025 together with Claude Sonnet 4, reviving the Opus tier after more than a year and marking Anthropic's pivot to long-horizon agentic work. It was pitched at sustained, multi-hour coding sessions — refactoring across large codebases, running in agent harnesses, and using tools in extended loops — rather than single-shot chat answers.

It posted 79.6% on GPQA Diamond and 72.5% on SWE-Bench Verified, roughly ten points above Claude 3.7 Sonnet on software engineering. Claude Opus 4.1 followed on August 5, 2025 as an incremental refinement, and the Opus line has since been Anthropic's flagship tier through Opus 4.5 and beyond.