Opus 4.5 Migration
FreeStreamline your transition to Opus 4.5 with ease.
Free · Opens the source repo
What Opus 4.5 Migration does
The Opus 4.5 Migration skill is designed for developers looking to upgrade their existing prompts and code from Claude Sonnet 4.0, Sonnet 4.5, or Opus 4.1 to the latest Opus 4.5 model. This skill provides a structured workflow to ensure that your codebase and API calls are updated efficiently, addressing the specific changes required for compatibility with Opus 4.5. It is particularly useful for teams that need to maintain their code while integrating new features and improvements from the latest model.
The migration process begins with identifying and updating model strings based on the platform being used. This skill provides a comprehensive guide to replacing outdated model strings with the correct Opus 4.5 equivalents for various platforms, including Anthropic API, AWS Bedrock, Google Vertex AI, and Azure AI Foundry. Additionally, it instructs users to remove unsupported beta headers and adjust parameters to align with the new model's requirements.
Beyond basic string updates, the skill also addresses known behavioral differences in Opus 4.5. It allows users to implement prompt adjustments only when necessary, ensuring that the migration does not inadvertently introduce issues. Users can apply fixes for overtriggering, over-engineering, code exploration, and frontend design based on specific user feedback, making the migration process adaptable to unique project needs.
This skill is ideal for developers and teams who are actively using prior versions of Claude models and need a reliable method to transition to Opus 4.5. It simplifies the migration process, allowing users to focus on enhancing their applications without getting bogged down in the minutiae of model updates.
When to use it
Use this skill when you need to update existing codebases and prompts from older Claude models to Opus 4.5.
When not to use it
This skill is not suitable for migrating Haiku 4.5 models or for users who do not have prior Claude models to update.
What you can build with it
Updating an Existing Codebase
A developer needs to transition their application from Opus 4.1 to Opus 4.5, ensuring all API calls are compatible.
Adjusting Prompts for New Behavior
A team encounters unexpected behavior in Opus 4.5 and uses the skill to adjust their prompts accordingly.
Removing Unsupported Features
A user needs to ensure that their code no longer references unsupported beta features before deploying to production.
How to install Opus 4.5 Migration
View source1. Install with the skills CLI
npx skills add davila7/claude-code-templates/claude-opus-4-5-migration --agent claude-code2. Or install it manually
Download the skill folder and drop it into ~/.claude/skills/ for all projects, or .claude/skills/ to scope it to one repo. Restart Claude Code so it picks up the new skill.
Anthropic's agentic coding CLI, and the reference implementation of Agent Skills. Drop a skill folder into ~/.claude/skills and Claude Code loads it automatically whenever a task matches the skill's description. Claude Code docs
Inside SKILL.md
Written by davila7Opus 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).
Frequently asked questions about Opus 4.5 Migration
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