Claude Opus 4.5 Migration

Anthropic's own Claude Code plugin for moving a codebase from Claude Sonnet 4, Sonnet 4.5 or Opus 4.1 to Claude Opus 4.5. It's a single skill: ask your agent to migrate, and it finds your model strings and API calls, updates them and sums up what it changed. What it does - Searches your codebase for model strings and API calls - Swaps in the Opus 4.5 model string for the Claude API, AWS Bedrock, Google Vertex AI or Azure AI Foundry - Removes the 1M-context beta header, which the skill says Opus 4.5 doesn't support yet, and leaves a comment saying why - Adds the effort parameter, set to high - Lists every change it made Prompt fixes, only when you ask Opus 4.5 behaves differently from earlier models, so the skill carries fixes for known issues. By default it only updates model strings; it applies these when you ask or report the problem: - Tools called too often: it softens forceful wording such as "CRITICAL" or "You MUST" in tool instructions - Extra files and abstractions: it adds a snippet that keeps solutions minimal - Fixes proposed without reading the code: it adds a snippet that has the model read the files first - Generic-looking frontend output: it adds a frontend design snippet - Trouble with the word "think" when extended thinking is off: it swaps in words like "consider" or "evaluate" How to install it In Claude Code, run /plugin marketplace add anthropics/claude-code, then /plugin install claude-opus-4-5-migration@claude-code-plugins. Then ask "Migrate my codebase to Opus 4.5". Good to know - It leaves Haiku models alone. - It targets Opus 4.5 only, not newer Claude models. - If anything feels off after the move, keep using the skill to adjust your prompts.

• “Migrate my codebase to Opus 4.5.”

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• “Update our Bedrock model IDs to Opus 4.5.”

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• “Opus 4.5 keeps calling tools it doesn't need. Can you adjust our prompts?”

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• “Since the switch it adds files and abstractions we didn't ask for. Fix the prompt.”

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• “It proposes fixes without reading the code first. Update our system prompt.”

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• “Our frontend output looks generic. Improve the design prompt.”

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