User Decodes Anthropic's Hidden Max x5/x20 Usage Limits and Billing Logic
Ohtince · reddit · 2026-08-24
A user reverse-engineered the internal billing model for Anthropic's Max x5 and x20 subscriptions after the company refused to disclose the metrics. Key findings include:
- Fable Model Surcharge: Fable consumes allowance at 4.25x (x5) and 6.5x (x20) the rate of Opus, significantly higher than its API list price (2x Opus).
- Design Principle: The plan is designed so that the worst-case API value strictly equals 100× the monthly subscription price. Using less Fable yields higher value (up to 150×).
- Upgrade Value: Upgrading from x5 to x20 doubles the token pool but only increases the Fable usage cap by 1.5×.
The post details the full formula and calculation process, suggesting the strict Fable cap may be due to limited inference supply.
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