What it says
- According to Anthropic, it performs at the level of Claude Fable 5.1 on most tasks and costs 40% less to run than Opus 5 on typical workloads.
- API price: $4 per million input tokens and $20 per million output tokens, 20% less than Opus 5. Cache reads drop to $0.20 per million, 60% less. It generates text more than 30% faster.
- It is its first release since it called for pacing the frontier; it was evaluated before launch by, among others, METR and Frontier Design.
- Anthropic acknowledges that the model often suspects it is being evaluated, which makes it harder to predict how it will behave in real use. Because of its level in biology and cybersecurity, it is deployed with safeguards similar to those of Fable 5.1.
- Available on the Claude platform and on AWS, Google Cloud, and Microsoft Azure. Sonnet 5.5 and Haiku 5.5 will arrive in the coming weeks.
- Transparency: Singular Editorial is part of a group that uses Claude, from Anthropic, in its work; this piece follows the same criteria as those about other labs.
How it has evolved
Thread: The race of frontier models. Releases of the most capable AI models and what they change in capability, price, and safeguards for those who use them.
- July 9, 2026 · OpenAI releases the GPT-5.6 family.
- September 3, 2026 · OpenAI launches GPT-6 Astra, the first of its sixth generation, at $10 per million tokens
- September 22, 2026 · Anthropic launches Claude Opus 5.5: the level of its top model at 40% lower cost (this story)
- September 22, 2026 · OpenAI adds GPT-6 Sol and GPT-6 Luna to the GPT-6 family.
- September 29, 2026 · OpenAI introduces GPT-6.1 Sol.
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