Sonnet 5.5 Lands: 30% Faster, Cheaper, and Now Claude's Free-Tier Engine
Anthropic's Claude Sonnet 5.5 delivers a 60-point jump on Terminal-Bench 4.0 while cutting per-task costs by up to 30%, making it the new default engine for Claude's free tier.
Anthropic has released Claude Sonnet 5.5, the second model in the Claude 5.5 family, positioned as a faster, lower-cost complement to Opus 5.5. It is priced identically to Sonnet 5 at $2 per million input tokens, $10 per million output tokens, and $0.20 per million cache reads, but Anthropic reports it typically needs far fewer tokens per task, yielding up to 30% lower cost per task. Output generation is 30%+ faster than Sonnet 5, making it the fastest Sonnet model to date. Cache writes are priced at $2.50 per million tokens, half the Opus 5.5 rate.
The most striking gains are in coding. On Terminal-Bench 4.0, an agentic coding evaluation, Sonnet 5.5 scores 70.6% versus Sonnet 5's 10.3%. On FrontierCode 1.1 at High effort it scores 46.2%, ten points above Sonnet 5 at the same setting, at roughly one fifteenth of the cost per task. On CursorBench 4.0 it reaches 55.5%, within about two points of Opus 5.5. Early testers noted that Sonnet 5.5 batches tool calls more aggressively than Sonnet 5, reducing steps and cost. On GDPval-AA v2.1, which tests real-world tasks across 44 occupations and nine industries, it scores 1844, nearly level with Opus 5.5's 1846 and about 400 points above Sonnet 5's 1449. It is also the first Sonnet model to beat Pokémon Red working only from screenshots.
Safety changes accompany the capability jump. Because Sonnet 5.5's cybersecurity capabilities are comparable to Opus 5's, it is the first Sonnet model to launch with cyber safeguards and fallbacks similar to those on Opus 5.5; higher-risk cybersecurity tasks visibly fall back to Sonnet 5. It also launches with safety classifiers that prevent reasoning extraction, a first for the Sonnet line, and expands preserved thinking so reasoning cannot be decoupled from the originating account. Biology safeguards remain the same as Sonnet 5's. On Anthropic's automated behavioral audit across roughly 1,850 scenarios, Sonnet 5.5 improves on or matches Sonnet 5 on most alignment measures.
Sonnet 5.5 is available on all platforms including AWS, Google Cloud, and Microsoft Azure, with zero data retention. Developers using Sonnet with thinking off must switch to the new between_tools setting before migrating; the model ID is claude-sonnet-5-5. Claude Haiku 5.5 is expected in the coming weeks.