Anthropic Releases Claude Sonnet 5.5 with Extended Thinking Capabilities

Anthropic has announced Claude Sonnet 5.5, bringing updated benchmark performance and extended thinking capabilities to its mid-tier AI model. The release has prompted technical evaluation regarding its reasoning token consumption, safeguard behavior, and benchmark results relative to Opus 5.5. Sonnet traditionally serves as Anthropic's high-efficiency workhorse model, so upgrading it with extended reasoning brings near-flagship performance to everyday developer workflows at lower costs. Understanding its balance of execution speed, safety restrictions, and reasoning token efficiency is vital for engineering teams building production AI pipelines. In benchmark evaluations like Terminal-Bench, Sonnet 5.5 scored 70.6 compared to Opus 5.5's 66.4, largely because Opus triggered a 10% fallback rate to backup models due to safety filters versus Sonnet's 1.5%. Technical users also observed that running extended thinking on maximum effort can consume up to 128,000 thinking tokens before timing out on heavy complex tasks.