What probably matters to youSection of the release
What
A new model, claude-opus-5-5 (display name "Opus 5.5"), has been added to Claude Code's model registry, with provider IDs across Bedrock, Vertex, and Foundry, a 1-million-token context window, and its own pricing tier. It's now recognized as a valid model ID throughout the client: in the model-name normalization table, the list of models allowed the 1M-token/auto-compact context window, and the model-family checks used for capabilities like fast mode and thinking.
The system prompt now lists "Opus 5.5: claude-opus-5-5" as the most capable model, in place of the previous "Opus 5" entry, and no longer ties fast mode's availability to "Opus 5/4.8."
Why
This makes Opus 5.5 usable across Claude Code's model selection, context-window handling, and pricing, and it becomes the model the system prompt now points to as the most capable option.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added sinceA small documentation edit on API usage primer for Claude touched a line naming claude-opus-5-5 after this was published.* Claude Opus 5.5 (`claude-opus-5-5`, adaptive thinking only, always on)claude_api_primersee the edit
Confirmed sinceAnthropic's documentation has since written up claude-opus-5-5, on claude-api-skill.When the scope is ambiguous (for example, a bare `/claude-api migrate to claude-opus-5-5`), the skill asks you to choose between the entire working directory, a specific subdirectory, or an explicit file list before editing any files. This…agents-and-tools/agent-skills/claude-api-skillsee the edit
How sure we are
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up claude-opus-5-5, on claude-api-skill.
Anthropic's release notes agreeAdded Claude Opus 5.5 (claude-opus-5-5), now the default Opus model — 1M context, $4/$20 per Mtok with $0.20/Mtok cache reads
