Anthropic released Claude Sonnet 5.5 on September 28 with unchanged token prices of $2 per million input tokens, $10 for output, and $0.20 for cache reads. Anthropic reports output generation more than 30% faster and up to 30% lower cost per task through fewer tokens. It is available as `claude-sonnet-5-5` on the Claude Platform and through AWS, Google Cloud, and Microsoft Azure, with zero data retention available. The benchmark table puts Sonnet 5.5 at 70.6% on Terminal-Bench 4.0, versus Sonnet 5's 10.3%. Opus 5.5's 66.4% is explicitly its highest result at Xhigh effort; the table does not support an equal-effort ranking. On GDPval-AA v2.1, Sonnet's 1844 rating nearly matches Opus's 1846. Anthropic says Sonnet complements Opus best at lower effort, where tasks cost less; higher settings can bring similar performance at similar cost. The strongest reason to trial Sonnet is cheaper completion of routine work, rather than a lower posted token price. Test it on a fixed document or coding assignment and count accepted outputs, corrections, and elapsed time. The maximum-effort score alone is a poor guide to an app running at medium effort. Defaults matter. Anthropic says Claude apps and Claude Code default to medium effort, while the Claude Platform defaults to high. Set the intended level explicitly before comparing bills. Existing integrations that turn thinking off need a configuration change to `between_tools`, and higher-risk cybersecurity requests may visibly fall back to Sonnet 5. Check both behaviors before replacing a model in an unattended workflow. Compare Sonnet 5.5 at medium and high effort on one task, including corrections and total cost. Anthropic’s source table, captured by IDG. Ratings, percentages, tool access, effort levels, and computer-use subsets differ; this is not an overall or equal-effort ranking. Footnote 1 marks Opus’s 66.4% Terminal-Bench result as its highest score at Xhigh. Footnote 2 reports Sonnet FrontierCode at 46.2% Max versus 52.1% Xhigh; Max incurred scope penalties or timeouts. Footnote 3 notes a fixed structured-output bug in the pre-release Sonnet deployment tested by Artificial Analysis. Footnote 4 notes a GPT-6 Sol visual-processing bug; official ratings may predate its fix. Credit: Anthropic; table captured by IDG. Source: Introducing Claude Sonnet 5.5, 2026-09-28. Claude Sonnet 5.5 System Card: Evaluation methods and safety results, including cybersecurity safeguards and fallback behavior. Migrating to Claude Sonnet 5.5: Explains the between_tools replacement for disabled thinking and other integration changes. Living documentation; publication date is not shown.