Model · Multimodal language model
Claude Opus 5.5
Anthropic's Claude Opus 5.5, the first model of the Claude 5.5 family released September 22, 2026, a text-and-image model with 1M-token context and always-on adaptive thinking, served through the Claude API and major cloud marketplaces.
- Developer
- Anthropic
- Distribution
- Developer API · Third-party hosting
- Artifact licensing
- Proprietary access
- License scope
- Reviewed release artifacts and mandatory terms; not an assessment of training code or training data openness.
- Licenses
- Anthropic Commercial Terms of Service
- Boundary
- This record represents the Claude Opus 5.5 release of September 22, 2026, the first model of the Claude 5.5 family with the pinned claude-opus-5-5 API identifier. The reviewed Opus 5 and Opus 4.8 lines, earlier Opus releases, and independent hosts are separate boundaries.
Risk statements
“CB-1” · Precautionary
On chemical and biological risks, we treat Opus 5.5 as having CB-1 capabilities (relating to the synthesis of non-novel weapons) but not CB-2 capabilities (relating to the synthesis of novel weapons).
- Risk areas
- Biological or chemical
- Covers
- The model itself
Read the developer's statement ↗ · 2026-10-07 · Research confidence: Medium
Anthropic names this release against “CB-1” in biological or chemical capability, as a precaution. The statement covers the model itself. This is the developer's own statement, not an Atlas risk rating.
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