Claude Opus 4.5 Migration — Automated Model Migration

Cross-Platform Model Migration

Migrates codebases from Claude 4.x to Opus 4.5 across four major platforms: Anthropic API, AWS Bedrock, Google Vertex AI, and Azure. Performs automated string replacement, header cleanup, prompt adjustment, and generates a comprehensive migration summary.

Skill

Platforms

Files

Language

🔄 Migration🌐 Multi-Platform📝 Prompt Tuning⚡ One-Shot

📚 What is this & why does it exist?

When Anthropic releases a new model version like Opus 4.5, every codebase using Claude needs to be updated — model identifiers change, API headers may need adjustment, and system prompts should be tuned for the new model's capabilities. This skill automates the entire process: it scans the codebase, detects which platform SDK is being used, performs all necessary string replacements, cleans up deprecated headers, adjusts prompts for Opus 4.5 improvements, and produces a summary of every change made. It's designed as a one-shot migration that handles everything in a single pass.

💡 Real-world analogy

Imagine upgrading the engine in a fleet of vehicles. Each vehicle might be a sedan (Anthropic API), a truck (AWS Bedrock), an SUV (Google Vertex), or a van (Azure). The new engine (Opus 4.5) fits all of them, but each vehicle type needs different mounting brackets, wiring harnesses, and calibration settings. This skill is the master mechanic who knows every vehicle type, does the swap, reconnects everything correctly, and hands you a detailed service report — all in one visit.

Architecture

flowchart TB
    subgraph Scan["Step 1: Codebase Scan"]
        START["Skill Auto-Invoked"] --> SCAN["Scan All Source Files"]
        SCAN --> DETECT["Detect Model References"]
    end
    subgraph Platform["Step 2: Platform Detection"]
        DETECT --> PD{"Which Platform?"}
        PD --> ANTH["Anthropic API"]
        PD --> AWS["AWS Bedrock"]
        PD --> GCP["Google Vertex AI"]
        PD --> AZ["Azure"]
    end
    subgraph Replace["Step 3: String Replacement"]
        ANTH --> R1["claude-3-* → claude-opus-4-5"]
        AWS --> R2["anthropic.claude-v3* → anthropic.claude-opus-4-5"]
        GCP --> R3["claude-3-*@* → claude-opus-4-5@20260301"]
        AZ --> R4["claude-3-* → claude-opus-4-5"]
    end
    subgraph Cleanup["Step 4: Header Cleanup"]
        R1 --> HC["Remove Deprecated Headers"]
        R2 --> HC
        R3 --> HC
        R4 --> HC
        HC --> VER["Update API Version Strings"]
    end
    subgraph Prompt["Step 5: Prompt Adjustment"]
        VER --> PA["Scan System Prompts"]
        PA --> TUNE["Tune for Opus 4.5 Capabilities"]
        TUNE --> TOKENS["Adjust Token Limits"]
    end
    subgraph Summary["Step 6: Summary"]
        TOKENS --> RPT["Generate Migration Report"]
        RPT --> DONE["Migration Complete"]
    end

Platform Support

☁️ Anthropic API (Direct)

Direct API calls using the Anthropic SDK. Replaces model strings in anthropic.messages.create() calls and updates the anthropic-version header.

Old: claude-3-opus-20240229, claude-3-5-sonnet-20241022
New: claude-opus-4-5-20260301
Header: anthropic-version: 2026-03-01

⚡ AWS Bedrock

Bedrock model IDs use a different naming convention. Also updates IAM policy references and inference profile ARNs.

Old: anthropic.claude-3-opus-20240229-v1:0
New: anthropic.claude-opus-4-5-20260301-v1:0
Region: Cross-region inference support

📌 Google Vertex AI

Vertex uses versioned model paths with @ separators. Updates both the model identifier and the publisher path.

Old: claude-3-opus@20240229
New: claude-opus-4-5@20260301
Endpoint: publishers/anthropic/models/

🔵 Azure

Azure deployment names and model references. Updates the deployment configuration and API version string.

Old: claude-3-opus deployment
New: claude-opus-4-5 deployment
API: api-version=2026-03-01

Migration Sequence

sequenceDiagram
    participant Trigger as Auto-Invoke
    participant Skill as Migration Skill
    participant FS as File System
    participant Report as Summary

    Trigger->>Skill: Skill auto-invoked on migration request
    Skill->>FS: Scan *.py, *.ts, *.js, *.json, *.yaml
    FS-->>Skill: 47 files with model references found

    Skill->>Skill: Detect platforms (Anthropic: 12, Bedrock: 8, Vertex: 5)
    
    loop For each file
        Skill->>FS: Read file content
        Skill->>Skill: Replace model identifiers
        Skill->>Skill: Clean deprecated headers
        Skill->>Skill: Update API versions
        Skill->>FS: Write updated file
    end

    Skill->>Skill: Scan system prompts in 6 files
    Skill->>FS: Adjust prompt token limits
    Skill->>FS: Tune prompts for Opus 4.5

    Skill->>Report: Generate migration summary
    Report-->>Trigger: 25 files modified, 3 platforms, 0 errors

Key Components

Component	File	Role
`claude-opus-4-5-migration`	`skills/claude-opus-4-5-migration/SKILL.md`	Main skill definition with migration logic and patterns
`platform-patterns`	`skills/claude-opus-4-5-migration/references/platform-patterns.md`	Regex patterns for each platform's model identifier format
`prompt-tuning`	`skills/claude-opus-4-5-migration/references/prompt-tuning.md`	Guidance on adjusting prompts for Opus 4.5 capabilities
`deprecated-headers`	`skills/claude-opus-4-5-migration/references/deprecated-headers.md`	List of deprecated headers and their replacements
`plugin.json`	`.claude-plugin/plugin.json`	Plugin manifest with skill registration

Replacement Patterns

Platform	Old Pattern	New Value
Anthropic	`claude-3-opus-20240229`	`claude-opus-4-5-20260301`
Anthropic	`claude-3-5-sonnet-20241022`	`claude-opus-4-5-20260301`
Anthropic	`claude-3-haiku-20240307`	`claude-opus-4-5-20260301`
Bedrock	`anthropic.claude-3-opus-*-v1:0`	`anthropic.claude-opus-4-5-20260301-v1:0`
Vertex	`claude-3-opus@*`	`claude-opus-4-5@20260301`
Azure	`claude-3-opus`	`claude-opus-4-5`

Interactions

Module	Interface	Data Exchanged
File System	Read/Write	Source files scanned and modified in-place
Anthropic API docs	Reference	Current model identifiers and API version strings
AWS Bedrock docs	Reference	Bedrock-specific model ARN formats
Vertex AI docs	Reference	Vertex model path and versioning convention
Claude Code Skill System	Auto-invocation	Triggered when migration-related prompts are detected

Directory Map

Source tree for Claude Opus 4.5 Migration

claude-opus-4-5-migration/
├── .claude-plugin/plugin.json          ← Plugin manifest
├── README.md                           ← Plugin documentation
└── skills/
    └── claude-opus-4-5-migration/
        ├── SKILL.md                    ← Main migration skill
        └── references/
            ├── platform-patterns.md    ← Platform-specific regex patterns
            ├── prompt-tuning.md        ← Opus 4.5 prompt optimization guide
            └── deprecated-headers.md   ← Deprecated header cleanup list

Configuration Reference

Parameter	Default	Description
`target_model`	claude-opus-4-5-20260301	Target model identifier for migration
`platforms`	["anthropic","bedrock","vertex","azure"]	Platforms to scan for (can be filtered)
`scan_extensions`	[".py",".ts",".js",".json",".yaml",".yml"]	File extensions to scan
`dry_run`	false	Preview changes without writing files
`adjust_prompts`	true	Whether to tune system prompts for Opus 4.5
`update_token_limits`	true	Adjust max_tokens for Opus 4.5 context window
`generate_report`	true	Produce a summary report after migration

Prompt Tuning

Opus 4.5 introduces improved capabilities that affect system prompt design:

📈 Extended Context

Opus 4.5 supports larger context windows. The skill updates max_tokens values and removes unnecessary context-saving workarounds from system prompts.

🧠 Enhanced Reasoning

Removes explicit chain-of-thought instructions that are now handled natively by the model. Simplifies verbose system prompts that over-specified reasoning steps.

🎨 Improved Formatting

Cleans up format-forcing instructions (e.g., "always respond in JSON") where Opus 4.5 handles structured output more reliably without them.