Claude Sonnet 5.5 (Adaptive Reasoning, Max Effort, Default Fallback)

Claude Sonnet 5.5 is the second model in Anthropic's Claude 5.5 family and a faster, lower-cost complement to Claude Opus 5.5. It targets well-scoped everyday tasks, coding, and polished documents, slides, and spreadsheets, and runs 30%+ faster than Claude Sonnet 5 while typically using far fewer tokens at the same $2/$10 per million input/output prices. It accepts text and image input with text output, supports multilingual and vision workloads, tool use, and adaptive thinking (Claude Platform default effort high; Claude Code and apps default medium). Context window is 1M tokens with 128K max output on the sync Messages API; reliable knowledge and training-data cutoffs are June 2026. Cache reads are $0.20 and 5-minute cache writes are $2.50 per million tokens. Capability scores are self-reported from the Claude Sonnet 5.5 System Card (Table 8.1.A and §8) and the launch announcement. Available on the Claude API as `claude-sonnet-5-5`.