claude-opus-4-5-migration
Migrate prompts and code from Claude Sonnet 4.0, Sonnet 4.5, or Opus 4.1 to Opus 4.5. Use when the user wants to update their codebase, prompts, or API calls to use Opus 4.5. Handles model string updates and prompt adjustments for known Opus 4.5 behavioral differences. Does NOT migrate Haiku 4.5.
When & Why to Use This Skill
The Claude Opus 4.5 Migration skill is a specialized developer utility designed to automate the transition of AI-powered applications from legacy Claude models (Sonnet 4.0, 4.5, and Opus 4.1) to the latest Opus 4.5. It streamlines the upgrade process by managing model string replacements across multiple cloud providers, cleaning up deprecated API headers, and providing expert-level prompt engineering adjustments to optimize for Opus 4.5's unique behavioral nuances.
Use Cases
- 1. Automated Codebase Migration: Scan and replace outdated Claude model strings with Opus 4.5 identifiers for Anthropic API, AWS Bedrock, Google Vertex AI, and Azure AI Foundry.
- 2. Prompt Optimization for Opus 4.5: Adjust system prompts to mitigate specific behavioral differences such as tool overtriggering, over-engineering, and 'thinking' sensitivity.
- 3. API Compatibility Cleanup: Identify and remove unsupported beta headers (e.g., 1M context) and configure the new 'effort' parameter to ensure seamless API integration.
- 4. Frontend Design Enhancement: Apply specialized prompt snippets to leverage Opus 4.5's improved capabilities in frontend aesthetics and UI code generation.
| name | claude-opus-4-5-migration |
|---|---|
| description | Migrate prompts and code from Claude Sonnet 4.0, Sonnet 4.5, or Opus 4.1 to Opus 4.5. Use when the user wants to update their codebase, prompts, or API calls to use Opus 4.5. Handles model string updates and prompt adjustments for known Opus 4.5 behavioral differences. Does NOT migrate Haiku 4.5. |
Opus 4.5 Migration Guide
One-shot migration from Sonnet 4.0, Sonnet 4.5, or Opus 4.1 to Opus 4.5.
Migration Workflow
- Search codebase for model strings and API calls
- Update model strings to Opus 4.5 (see platform-specific strings below)
- Remove unsupported beta headers
- Add effort parameter set to
"high"(seereferences/effort.md) - Summarize all changes made
- Tell the user: "If you encounter any issues with Opus 4.5, let me know and I can help adjust your prompts."
Model String Updates
Identify which platform the codebase uses, then replace model strings accordingly.
Unsupported Beta Headers
Remove the context-1m-2025-08-07 beta header if present—it is not yet supported with Opus 4.5. Leave a comment noting this:
# Note: 1M context beta (context-1m-2025-08-07) not yet supported with Opus 4.5
Target Model Strings (Opus 4.5)
| Platform | Opus 4.5 Model String |
|---|---|
| Anthropic API (1P) | claude-opus-4-5-20251101 |
| AWS Bedrock | anthropic.claude-opus-4-5-20251101-v1:0 |
| Google Vertex AI | claude-opus-4-5@20251101 |
| Azure AI Foundry | claude-opus-4-5-20251101 |
Source Model Strings to Replace
| Source Model | Anthropic API (1P) | AWS Bedrock | Google Vertex AI |
|---|---|---|---|
| Sonnet 4.0 | claude-sonnet-4-20250514 |
anthropic.claude-sonnet-4-20250514-v1:0 |
claude-sonnet-4@20250514 |
| Sonnet 4.5 | claude-sonnet-4-5-20250929 |
anthropic.claude-sonnet-4-5-20250929-v1:0 |
claude-sonnet-4-5@20250929 |
| Opus 4.1 | claude-opus-4-1-20250422 |
anthropic.claude-opus-4-1-20250422-v1:0 |
claude-opus-4-1@20250422 |
Do NOT migrate: Any Haiku models (e.g., claude-haiku-4-5-20251001).
Prompt Adjustments
Opus 4.5 has known behavioral differences from previous models. Only apply these fixes if the user explicitly requests them or reports a specific issue. By default, just update model strings.
Integration guidelines: When adding snippets, don't just append them to prompts. Integrate them thoughtfully:
- Use XML tags (e.g.,
<code_guidelines>,<tool_usage>) to organize additions - Match the style and structure of the existing prompt
- Place snippets in logical locations (e.g., coding guidelines near other coding instructions)
- If the prompt already uses XML tags, add new content within appropriate existing tags or create consistent new ones
1. Tool Overtriggering
Opus 4.5 is more responsive to system prompts. Aggressive language that prevented undertriggering on previous models may now cause overtriggering.
Apply if: User reports tools being called too frequently or unnecessarily.
Find and soften:
CRITICAL:→ remove or softenYou MUST...→You should...ALWAYS do X→Do XNEVER skip...→Don't skip...REQUIRED→ remove or soften
Only apply to tool-triggering instructions. Leave other uses of emphasis alone.
2. Over-Engineering Prevention
Opus 4.5 tends to create extra files, add unnecessary abstractions, or build unrequested flexibility.
Apply if: User reports unwanted files, excessive abstraction, or unrequested features. Add the snippet from references/prompt-snippets.md.
3. Code Exploration
Opus 4.5 can be overly conservative about exploring code, proposing solutions without reading files.
Apply if: User reports the model proposing fixes without inspecting relevant code. Add the snippet from references/prompt-snippets.md.
4. Frontend Design
Apply if: User requests improved frontend design quality or reports generic-looking outputs.
Add the frontend aesthetics snippet from references/prompt-snippets.md.
5. Thinking Sensitivity
When extended thinking is not enabled (the default), Opus 4.5 is particularly sensitive to the word "think" and its variants. Extended thinking is enabled only if the API request contains a thinking parameter.
Apply if: User reports issues related to "thinking" while extended thinking is not enabled (no thinking parameter in request).
Replace "think" with alternatives like "consider," "believe," or "evaluate."
Reference
See references/prompt-snippets.md for the full text of each snippet to add.
See references/effort.md for configuring the effort parameter (only if user requests it).