tl;dr: Anthropic released Claude Sonnet 5.5, a faster (30%+) and cheaper (up to 30% less per task) upgrade to Sonnet 5, priced identically at $2/$10 per million input/output tokens. It shows major gains in agentic coding (70.6% vs 10.3% on Terminal-Bench 4.0) and approaches Opus 5.5 performance on several benchmarks while remaining a lower-cost complement for everyday tasks. It's also the first Sonnet model to ship with cybersecurity safeguards and anti-distillation classifiers, reflecting its significantly expanded capabilities.