Anthropic Claude Opus 5, the new-generation flagship. It approaches the frontier intelligence of Fable 5 for roughly half the cost, which makes it the best-value high-end option. Against Opus 4.8 it roughly doubles coding performance on Frontier-Bench, scores about three times the next-best model on novel problem solving, and leads clearly on computer use and scientific research; charts and interactive output are noticeably better too. Its most praised trait is thoroughness: it verifies its own work, iterates carefully, and catches logical errors before acting. Supports very long context for whole-codebase or multi-document analysis, plus a reasoning-effort dropdown (five levels, default high), an option to show the thinking process, web search, and image and document upload. Reserve it for the hardest work such as large refactors, complex architecture design, and deep research; use Sonnet 5 or Haiku 4.5 for light everyday chat.