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Files

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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Opus Fast Model Configuration

Issue

The "Opus fast" model deployment is currently limited to 200,000 tokens, causing errors like:

Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"prompt is too long: 282789 tokens > 200000 maximum"},"request_id":"req_011CVZ3fj1gSV2ZBzHGVnRrA"}

Solution

Environment Variable Configuration

Claude Code uses environment variables to control model aliases. To configure the fast Opus deployment with extended context length, set the following environment variable:

# Configure Opus alias to use the fast deployment with extended context
export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"

Extended Context Configuration

The fast Opus deployment should support extended context length beyond the default 200k tokens. The recommended configuration:

# For environments supporting extended context (up to 2M tokens)
export ANTHROPIC_DEFAULT_OPUS_MODEL="claude-opus-4-5-20251101-fast"
export ANTHROPIC_OPUS_CONTEXT_LIMIT="1000000"  # 1M tokens as intermediate step

VSCode Configuration

For VSCode users wanting to use the fast Opus model, add these to your settings or environment:

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

Verification

To verify the configuration is working:

Check that the environment variable is set:
```
echo $ANTHROPIC_DEFAULT_OPUS_MODEL
```
Test with a large context that previously failed (>200k tokens)
Monitor for the absence of "prompt is too long" errors

Background

Based on internal discussions, the prod fast Opus deployment is available and should:

Be properly configured in the model selector
Have awareness of its extended context length
Support significantly more than the 200k token limit

The current limitation appears to be a configuration issue where Claude Code is not aware of the extended context capabilities of the fast deployment.

Other relevant environment variables for model configuration:

ANTHROPIC_DEFAULT_SONNET_MODEL: Controls the Sonnet model alias
ANTHROPIC_MODEL: Used for Bedrock configurations
ANTHROPIC_SMALL_FAST_MODEL: Used for fast model configurations

Status

Identified the configuration issue
Documented the solution
Verify with Claude Code development team
Test in production environment

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