Claude Opus 5.5
AnthropicClaude Opus 5.5 is Anthropic's current flagship Opus model for complex agentic coding, deep analytical reasoning, and enterprise workloads — delivering significant improvements in test-time compute scaling, instruction precision, and tool-call reliability over Opus 5. 1M context window, 128K max output. Adaptive thinking is ON by default (omitting the thinking parameter runs adaptive); disabling thinking is only allowed at effort 'high' or lower. Raw thinking tokens are never returned. Full effort ladder (low/medium/high/xhigh/max), 512-token prompt-cache minimum, elevated cybersecurity safeguards. Separate rate-limit bucket from the Opus 4.x pool.