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best practice

Recalibrate Budgeting for the 30% Higher Token Density

Accurately predict API costs by using the Fable-specific tokenizer.

Always run your prompts through the Token Counting API specifically for 'claude-fable-5' to account for the 30% increase in token density.

Claude

The Scenario

You are managing a budget-sensitive project and need to accurately predict the cost of running large-scale prompts using the new Fable 5 model.

Before & after

The old way

Users often estimated token counts based on old models, which could lead to budget overruns or hitting limits unexpectedly, taking 15 minutes of manual calculation.

With AI

Use the token counting API with 'model: claude-fable-5' to see exact costs in seconds before hitting 'send' on a massive batch.

The Prompt

// Use the Token Counting API
curl https://api.anthropic.com/v1/token_count \
  -H "x-api-key: [YOUR_API_KEY]" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-fable-5",
    "messages": [{"role": "user", "content": "[PASTE_YOUR_LONG_PROMPT_HERE]"}]
  }'

The new tokenizer produces about 30% more tokens for the same text compared to older versions, so precise measurement is critical for cost control.

Source

Claude Platform - Claude API Docs
"Compared to models before Claude Opus 4.7, the same text produces roughly 30% more tokens. Use the token counting API."