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Frontier flagship models

Claude Sonnet 5.5

Anthropic

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Published benchmark scores: Artificial Analysis Intelligence Index v4.3.256 — 3rd of 216 models
combined score across ten reasoning and knowledge tests · tested: max with fallback
Artificial Analysis · 28 September 2026 · independent
Measured at 141.9 tokens per second output speed.
Figures copied from the sources above, checked 17 September 2026.
Cost: API $2 in / $10 out per million tokens; Claude plans from free to $100/month.
Performance: Anthropic's faster, lower-cost complement to Opus 5.5, announced 28 September 2026, aimed at well-scoped everyday tasks — fixing bugs and producing documents, slides and spreadsheets. The launch post reports 70.6% on Terminal-Bench 4.0 agentic coding (up from 10.3% for Sonnet 5), two points below Opus 5.5 on GDPval-AA, and outputs generated 30%+ faster than Sonnet 5; benchmark figures are the maker's own, so check independent leaderboards for a specific task.
Use it for: Everyday coding and bug fixes
Polished documents, slides and spreadsheets
High-volume work that doesn't need Opus 5.5's sustained judgment
Keep in mind: The first Sonnet model to launch with cyber safeguards like those on the lab's most capable models, per the announcement; heavier use on Claude plans follows usage-window limits.