They weren't going to let people have it that cheap for very long. The plan was to offer it on subscription plans for a couple weeks, then move to usage-based billing, which is much more expensive for a usage pattern that comes anywhere near the subscription limits.

Keeping a single instance of Fable busy for a full day would probably cost a thousand dollars at standard API rates, and some agentic coding workflows run many agents in parallel. Companies have just recently started to figure out that rewarding employees for how many tokens they use may be a waste of money, but Anthropic is hoping to cash in before they all do.