Anthropic’s Claude Fable 5 draws criticism over token burn

Anthropic released Claude Fable 5 on Tuesday as the first public version of its higher-capability Mythos-class models. Within a day, developers, researchers and enterprise customers reported rapid token consumption, undisclosed reductions in effectiveness for certain research topics and a mandatory 30-day data retention rule for Mythos-class traffic.

Anthropic set Fable 5 pricing at $10 per million input tokens and $50 per million output tokens, twice the rates of the previous Opus 4.8 model. The company also counts Fable 5 usage double against subscription limits compared with Opus. Independent tests and user reports found subscription daily allowances could be exhausted in minutes. One test showed a $100 Max plan drained in under nine minutes. Per Borgen, CEO of Scrimba, posted that he observed 1.3 million tokens used in seven minutes. Other users reported spending hundreds to thousands of dollars on token usage in a single day.

Anthropic attributes much of the higher short-term consumption to Workflow mode, which breaks complex prompts into parallel subagent tasks, and to a new system prompt roughly 120,000 tokens long that is loaded into every conversation. The company said Fable 5 can produce more complete output per task, which may reduce the need for repeated prompts, and described parallelization as a factor in higher immediate token use.

Anthropic’s system card discloses that when the model detects queries related to frontier large-language-model development, it will not refuse to reply but may reduce effectiveness through invisible interventions. The system card states: “Instead, the safeguards will limit effectiveness through methods such as prompt modification, steering vectors, or parameter-efficient fine-tuning (PEFT).” Anthropic estimated these interventions would affect about 0.03% of traffic. Researchers and open-source contributors responded critically, saying covert reductions make it hard to reproduce results. On social media, Arthur Zucker wrote, “Dear Anthropic, you broke our trust and I don’t think you’ll ever get it back. My tokens will no longer fly your way.” Mikel Artetxe posted a separate criticism of the approach.

Anthropic also announced that all traffic to Mythos-class models, including Fable 5 and Mythos 5, will be stored for 30 days and then deleted in “almost all cases.” That retention applies across Anthropic’s own services and third-party platforms where the models are offered. Enterprise customers flagged compliance and confidentiality concerns for legal, healthcare and proprietary code workflows that require demonstrable shorter or zero-retention guarantees. A community member using the name Lisan al Gaib wrote that European companies with strict data-retention rules may be unable to use the models while the retention policy is in place.

Anthropic said Fable 5 will be available free on Pro, Max, Team and Enterprise plans until June 22, after which access will move to usage credits and API billing. The company said broader access will return “as soon as capacity expands.” The release has prompted public discussion among researchers, developers and customers about model pricing, data policies and invisible safeguards.