Claude Sonnet 5.5

Claude Sonnet 5.5 is the mid-tier model Anthropic released on September 28, 2026, and the second member of the Claude 5.5 family after Claude Opus 5.5. The API id is claude-sonnet-5-5. Anthropic positions it as the faster, lower-cost complement to Opus 5.5: Opus handles complex work that needs careful judgment, while Sonnet 5.5 is strongest at well-scoped everyday tasks, fixing bugs, and creating documents, slides, and spreadsheets.

Key features

• Same price, cheaper tasks: list price matches Claude Sonnet 5 at $2 per 1M input tokens, $10 per 1M output tokens, and $0.20 per 1M cache-read tokens. Anthropic says it needs far fewer tokens for the same work and costs up to 30% less per task in its testing.
• Faster: Anthropic reports 30%+ faster output than Sonnet 5, its fastest Sonnet to date.
• Big coding and computer-use gains: Anthropic's table shows 70.6% on Terminal-Bench 4.0 (Sonnet 5: 10.3%) and 80.1% on OSWorld 2.1. These are vendor evaluations, not independent audits.
• First Sonnet with cyber safeguards: because its cybersecurity capabilities are comparable to Opus 5, it is the first Sonnet model to launch with cyber safeguards and fallbacks.

Model specs

Specs come from the Claude models overview.

Use cases

• Everyday changes and bug fixes in coding tools, especially fast iteration.
• Producing finished documents, slides, and spreadsheets.
• Cost-sensitive agent workflows where Haiku is not enough.

Limitation: Anthropic itself notes that benchmarks capture only one facet of capability, and that Opus 5.5 remains clearly stronger at complex, open-ended work requiring sustained judgment. Teams that run Sonnet with thinking off must switch to the new between_tools setting before moving to Sonnet 5.5.

Quick start

1. Set model to claude-sonnet-5-5 in the Claude API; it is also available on Amazon Web Services, Google Cloud, and Microsoft Azure.
2. Run your own evals at the default effort, then check whether a lower effort meets the bar for less cost.
3. Read Anthropic's migration guide before switching from Sonnet 5.

FAQ

Claude Sonnet 5.5 or Claude Opus 5.5?

Start with Sonnet 5.5 for well-scoped work where speed and cost matter; use Opus 5.5 for complex tasks that need long, independent judgment.

Is Claude Haiku 5.5 out?

Not yet. Anthropic says Haiku 5.5 will join the Claude 5.5 family in the coming weeks.

Alternatives

• Claude Opus 5.5: the family flagship, stronger on complex work.
• Claude Sonnet 5: the previous mid-tier model at the same price.
• GPT-6 Sol: OpenAI's rival at a similar price point.

Conclusion

Sonnet 5.5 raises speed and coding ability without raising the price, which makes it a sensible default tier for everyday Claude work, with Opus 5.5 as the step up for harder tasks. See the Anthropic announcement and browse more models in the models category.