Claude Code release notes: 2.1.280 adds Opus 5.5

Claude Code 2.1.280 adds Claude Opus 5.5 with a one-million-token context window and lower API prices than Opus 5. Context is the material a model can have available in a request, such as code, instructions, and previous messages.

The release was published on September 22. When checked on September 24, 2.1.281 was the latest version on GitHub and npm; model support arrived in 2.1.280.

Sources: Claude Code 2.1.280 release notes. Claude Code 2.1.281. npm registry.

Select Opus 5.5 in Claude Code

Human step: Update with claude update in your terminal. Opus 5.5 requires Claude Code 2.1.280 or later.

With a direct Anthropic API connection, you can then type /model claude-opus-5-5 in Claude Code. This switches models and saves your choice as the default for new sessions. To switch only for the current session, open /model instead, highlight the model, and press s.

The opus alias, a short name for a model version, now points to Opus 5.5 on the Anthropic API, Claude Platform on AWS, Amazon Bedrock, and Google Cloud's Agent Platform. Microsoft Foundry is an exception: its alias still points to Opus 4.6. Availability of a new model therefore does not mean the same alias selects it on every provider. Custom model settings and organization restrictions still apply.

Source: Claude Code: model aliases, version requirements, and model selection.

API pricing and limits

Anthropic lists the following standard Opus 5.5 prices per million tokens, the units of text the model processes:

• Input: US$4.
• Output: US$20.
• Cache reads: US$0.20. This covers reuse of previously stored context.

Fast mode has separate pricing: US$8 for input and US$40 for output per million tokens. API prices are not Claude subscription prices; other cloud providers determine their own billing.

Opus 5.5 does not allow thinking to be turned off completely. Anthropic also describes automatic routing to other models for certain tasks, including cybersecurity and biology. A selected model name therefore does not guarantee that Opus 5.5 answers every such request.

Sources: Anthropic: Introducing Claude Opus 5.5, pricing and limits. Claude Code: third-party provider pricing.