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Claude 52817e8c22 Fix context length configuration for Opus fast model

Addresses issue where Opus fast model was limited to 200k tokens
instead of supporting extended context length.

Changes:
- Add OPUS_FAST_CONFIGURATION.md with environment variable setup
- Add FAST_MODEL_CONFIG.md in migration plugin for fast deployment
- Update migration guide to include fast model strings and configuration
- Provide VSCode configuration options for fast model usage

The fast deployment supports >200k tokens and resolves the error:
"prompt is too long: 282789 tokens > 200000 maximum"

Configuration: Set ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"

2025-11-27 20:52:21 +00:00

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Fast Opus 4.5 Model Configuration

Issue

The standard Opus 4.5 configuration is limited to 200,000 tokens, causing failures with larger contexts.

Solution: Fast Opus Deployment

Environment Variable Configuration

To use the fast Opus deployment with extended context length, configure Claude Code with:

# Set the Opus alias to use the fast deployment
export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"

Model String Updates for Fast Deployment

Platform	Fast Opus 4.5 Model String
Anthropic API (1P)	`claude-opus-4-5-20251101-fast`
AWS Bedrock	`anthropic.claude-opus-4-5-20251101-fast-v1:0`
Google Vertex AI	`claude-opus-4-5-fast@20251101`
Azure AI Foundry	`claude-opus-4-5-20251101-fast`

Context Length Configuration

The fast deployment supports extended context. Configure the context limit:

# Extended context configuration (up to 1M tokens)
export ANTHROPIC_OPUS_CONTEXT_LIMIT="1000000"

Integration with Migration Tool

When migrating to Opus 4.5 with extended context requirements:

Use the fast model strings above instead of standard ones
Set the environment variable for Opus alias
Configure extended context limit
Test with large contexts (>200k tokens)

VSCode Configuration

For VSCode extension users:

{
  "claude-code.environmentVariables": {
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "claude-opus-4-5-20251101-fast",
    "ANTHROPIC_OPUS_CONTEXT_LIMIT": "1000000"
  }
}

Verification

Test the configuration with a prompt that exceeds 200k tokens to ensure the error:

prompt is too long: 282789 tokens > 200000 maximum

is resolved.

When to Use Fast vs Standard

Use Fast: For large codebases, extensive context analysis, long conversations
Use Standard: For typical development tasks with smaller context requirements

The fast deployment trades some response speed for much higher context capacity.

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