Claude Opus 5.5
Anthropic · 2026-09-22
Claude Opus 5.5 is Anthropic's September 22, 2026 model for long-running coding and knowledge work. Adaptive thinking is always on, with low, medium, high, xhigh, and max effort and medium as the default. Production safeguards can route flagged requests to fallback models. The published knowledge cutoff is June 2026, without day precision.