Anthropic · Wednesday, September 23, 2026
Anthropic launches Claude Opus 5.5 with system card and new safeguards
The File desk · Sep 23, 2026, 10:30 AM UTC
Status
Confirmed (Anthropic news post + system card, Sept. 22, 2026)
On Tuesday, Sept. 22, 2026, Anthropic introduced Claude Opus 5.5 — application programming interface (API) ID claude-opus-5-5 — calling it the first model in the Claude 5.5 family. The company says it performs about as well as Claude Fable 5.1 on most work and costs about 40% less to run than Opus 5 at default settings. List prices are $4 per million input tokens and $20 per million output tokens, with cache reads at $0.20. Anthropic says outside evaluators including Frontier Design and METR tested the model before release, and that a Sept. 22 system card accompanies the launch. Because the company rates Opus 5.5 comparable to Claude Mythos 5.1 in biology and cybersecurity, it is deploying similar safeguards to Fable 5.1, with Life Sciences and Cyber verification programs for vetted users. Sonnet 5.5 and Haiku 5.5 are said to follow in coming weeks. The model is available on Anthropic’s platform and on Amazon Web Services, Google Cloud, and Microsoft Azure.
On Tuesday, Sept. 22, 2026, Anthropic introduced Claude Opus 5.5.
The application programming interface (API) ID is claude-opus-5-5. Anthropic calls it the first model in the Claude 5.5 family.
The company says it performs about as well as Claude Fable 5.1 on most work and costs about 40% less to run than Opus 5 at default settings.
List prices are $4 per million input tokens and $20 per million output tokens, with cache reads at $0.20.
Anthropic says outside evaluators including Frontier Design and METR tested the model before release.
A system card dated Sept. 22 accompanies the launch.
Because the company rates Opus 5.5 comparable to Claude Mythos 5.1 in biology and cybersecurity, it is deploying similar safeguards to Fable 5.1, with Life Sciences and Cyber verification programs for vetted users.
Sonnet 5.5 and Haiku 5.5 are said to follow in coming weeks.
The model is available on Anthropic’s platform and on Amazon Web Services, Google Cloud, and Microsoft Azure.
What is still unknown or disputed
- Independent replication of Anthropic’s benchmark tables; exact cloud-region rollout timing.
Primary sources
Every claim in this story is drawn from the documents below. If a fetch failed, that is recorded on the card.
Source 1
Introducing Claude Opus 5.5
Anthropic · September 22, 2026
We’re introducing Claude Opus 5.5, the first model in our new Claude 5.5 family. It performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5.
https://www.anthropic.com/news/claude-opus-5-5
Source 2
Claude Opus 5.5 System Card
Anthropic · September 22, 2026
System Card: Claude Opus 5.5, dated September 22, 2026 (company system card)
https://www-cdn.anthropic.com/fc1b44717c85dc068bc6ba5024219938094694bd/Claude%20Opus%205.5%20System%20Card.pdf