Claude Sonnet 5.5
Anthropic · 2026-09-28
Claude Sonnet 5.5 is Anthropic's September 28, 2026 model for coding and professional work. Adaptive thinking is on by default with high effort; low, medium, high, xhigh, and max are supported. The between_tools setting disables up-front thinking at high effort or below. Provider fallbacks can route declined requests to Sonnet 5. Its published June 2026 knowledge cutoff has no day precision.