Anthropic released Claude Sonnet 5.5 on September 28, 2026, six days after Opus 5.5 and the second model in the 5.5 family. The price did not move: 2 dollars per million input tokens and 10 per million output, the same as Sonnet 5. Anthropic says it runs more than 30% faster and costs up to 30% less per task. The more interesting number is that it scores 70.6% on Terminal-Bench 4.0 against Opus 5.5’s 66.4%, while costing half as much per token.
Wait, the cheaper model beats the expensive one?
On that specific benchmark, at that specific setting, yes. Sonnet 5.5’s 70.6% on Terminal-Bench 4.0 is above Opus 5.5’s 66.4% at its highest effort setting. Both headline scores use the most expensive configuration, which is the caveat that matters. Terminal-Bench measures agentic command-line work, not general reasoning, so this is not a claim that Sonnet is smarter overall.
Still, it is a real result and it mirrors what happened at DeepSeek, where V4.1 Flash outperformed the larger V4-Pro flagship on coding. Cheaper models beating expensive ones on agentic tasks is becoming a pattern rather than an anomaly.
Where does the 30% saving come from?
Not from the price, which is unchanged. The claim is that Sonnet 5.5 needs fewer tokens to finish the same work, so the per-task bill drops even at the same per-token rate. That is a real effect if it holds on your workload, and it is worth measuring rather than assuming. Artificial Analysis measured higher task costs than Sonnet 5 at maximum effort, which cuts against the headline.
The full rate card: 2 dollars input, 10 output, 0.20 cache reads, 2.50 cache write at five minutes, 4 dollars cache write at one hour, and 50% off on the Batch API. Opus 5.5 sits at 4 and 20. Context window is 1 million tokens with 128,000 max output. Available on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry as claude-sonnet-5-5.
One pricing detail worth knowing
Anthropic describes 2 and 10 as the same pricing as Sonnet 5, and that is accurate, but there is history. Those rates were originally sold as introductory pricing due to rise to 3 and 15. Anthropic made them permanent instead. So the comparison is honest, though it is a comparison to a promotional rate that stuck rather than to an original list price.
The safety addition nobody is talking about
Sonnet 5.5 is the first Sonnet to ship with the cyber restrictions Anthropic previously reserved for its most capable models, and the first with classifiers that stop its reasoning being extracted. That second part has a specific trigger: researchers recently decoded 315,320 thinking blocks from publicly posted agent traces. Reasoning traces leaking is a real exposure, and this is a direct response.
Applying frontier-tier cyber limits to a mid-tier model also fits the restricted-access direction seen in Google’s Fairwind Program. One awkward footnote: Claude suffered a partial outage the day after this launched, which is the kind of thing that makes a two-models-in-seven-days cadence worth watching.
