Anthropic: Opus 5.5 costs less per token, and keeps the high-end guardrails
On 22 September 2026, Anthropic announces Claude Opus 5.5. The listed price is 4 dollars per million input tokens and 20 output, 20 percent less than Opus 5. Cache reads are 0.20, announced 60 percent lower. On biology and cyber, the page says guardrails close to those of Mythos.
Getting started
Original AI-generated illustration · SecuFocus
At a glance
Key points
Cheaper does not mean local. Opus 5.5 remains a hosted Claude. The page says it is comparable to Mythos 5.1 in biology and cybersecurity, and deploys it with guardrails of the same order. We did not read the system card as a second source.
What changes
The page is dated 22 September 2026. Opus 5.5 is the first model in the 5.5 family. Anthropic presents it at the level of Fable 5.1 on most work, and 40 percent cheaper to run than Opus 5. The priced detail is narrower: 4 and 20 dollars per million, against an Opus 5 that costs 20 percent more on those tokens, and 0.20 for cache, announced 60 percent lower.
External evaluators are named, Frontier Design and METR, for a test before release. The story of a 680,000-line migration in less than a day is a tester cited by Anthropic. It is not a SecuFocus trial.
What leaves
The code you send to Opus 5.5 leaves for Anthropic. The cheaper cache makes agent round trips less expensive. It assumes the context was already sent.
The page says Opus 5.5 is comparable to Mythos 5.1 in biology and cybersecurity, and that it ships with similar guardrails. A publisher’s guardrail is not a wall on your machine. It says what the service claims to refuse. It does not say which files left your repository.
What we did not verify
We did not open the system card, check the 40 percent, or call the API. The names Frontier Design and METR are the page’s. We did not read their reports.
The decision
If you pay for Opus, the new figures are 4, 20 and 0.20. If you give it a sensitive repository, the price does not change the question: the repository leaves. The announced guardrails do not bring it back.
Check and explore
Sources for this article
Numbers connect each reference to the passages that use it. Dates show when the documentation was consulted.
- Claude Opus 5.5, Anthropic ↗anthropic.com ·
This article draws on the sources above. The exercises are for you to try on your devices; SecuFocus does not present them as tests carried out by its editorial team. Interfaces and features can change. Method and corrections.
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