Anthropic releases Claude Sonnet 5.5, 30% faster than Sonnet 5 at the same $2 input price

What Anthropic announced

Anthropic released Claude Sonnet 5.5 on 28 September 2026, six days after Claude Opus 5.5. The announcement presents it as a faster, lower-cost complement to Opus 5.5. Anthropic says it is strongest at well-scoped everyday tasks, fixing bugs, and creating documents, slides and spreadsheets. It runs more than 30% faster than Claude Sonnet 5 and, in Anthropic's testing, costs up to 30% less per task because it needs fewer tokens.

The model overview lists a 1 million token context window, 128,000 max output tokens, adaptive thinking and a June 2026 knowledge cutoff. Default effort is medium in Claude Code and the Claude apps and high on the Claude Platform. Developers who ran Sonnet with thinking off need to move to a new between_tools setting before switching.

How much Claude Sonnet 5.5 costs

Sonnet 5.5 keeps Sonnet 5's list price of $2 per million input tokens and $10 per million output tokens. Cache reads cost $0.10 per million tokens, half of Sonnet 5's $0.20, and cache writes cost $2.50. That is half of Opus 5.5 on every line of the price table, where Opus 5.5 costs $4 input, $20 output and $0.20 for cache reads.

Anthropic argues that the real saving comes from token use. On several benchmarks, it says, Sonnet 5.5 at low or medium effort beats Sonnet 5's best score for about a tenth of the cost per task. Customers quoted in the announcement report similar effects, but those are vendor-selected testimonials.

What Anthropic claims on performance and safety

In Anthropic's table, Sonnet 5.5 scores 70.6% on Terminal-Bench 4.0, against 10.3% for Sonnet 5 and 66.4% for Opus 5.5. It reaches 55.5% on CursorBench 4.0, 80.1% on OSWorld 2.1 and 1844 Elo on GDPval-AA v2.1, two points below Opus 5.5. Anthropic says it is the first Sonnet model to beat Pokemon Red working only from screenshots. It also says Opus 5.5 remains clearly stronger at complex, open-ended work that needs sustained judgment.

Because its cyber capabilities are comparable to Opus 5, Sonnet 5.5 is the first Sonnet model to launch with cyber safeguards. Higher-risk security tasks visibly fall back to Sonnet 5, while routine bug fixing is unaffected. Biology safeguards are the same as Sonnet 5's. It is also the first Sonnet model with classifiers that block reasoning extraction, part of Anthropic's defence against distillation attacks.

What to watch next

Anthropic said Claude Haiku 5.5, built for high-volume and cost-sensitive work, would follow in the coming weeks. The model overview says Sonnet 5.5 will not be retired before 28 September 2027. The earlier Claude Opus 5.5 release explains the shared safeguards, and prices are tracked on the AI model release tracker and under AI Models.

Questions people ask

How much does Claude Sonnet 5.5 cost?

$2 per million input tokens and $10 per million output tokens, the same as Sonnet 5, with cache reads cut to $0.10 per million.

How does Claude Sonnet 5.5 compare with Claude Opus 5.5?

It costs half as much per token. Anthropic's benchmarks put it close to Opus 5.5 on several tests, but the company says Opus 5.5 is still stronger at complex, open-ended work.

What is the model ID of Claude Sonnet 5.5?

claude-sonnet-5-5 on the Claude Platform, and anthropic.claude-sonnet-5-5 on Amazon Bedrock, according to Anthropic's model overview.

Sources

1. Introducing Claude Sonnet 5.5 (Anthropic, 28 Sep 2026)
2. Models overview (Anthropic, 28 Oct 2026)