Claude Fable 5 completes Stripe's two-month migration in one day
Anthropic released Claude Fable 5 on June 9th with no preview period, and Stripe used it to complete a 50-million-line Ruby codebase migration in one day — a task estimated to take their entire team two months.
Score breakdown
The Stripe demonstration — a 50-million-line codebase migration completed in one day versus an estimated two months — is the concrete case the post uses to illustrate Fable 5's positioning as a model for sustained, long-context, multi-step work rather than short demos.
- 01Anthropic released Claude Fable 5 on June 9th with no preview period or waitlist
- 02Stripe used Fable 5 to complete a 50-million-line Ruby codebase migration in one day, a task estimated at two months for their full team
- 03Fable 5 sits above Opus in Anthropic's model lineup
Anthropic dropped Claude Fable 5 on June 9th with no preview period or waitlist, positioning it above Opus in the company's model lineup. The headline use case came from Stripe, which used Fable 5 to handle a Ruby codebase migration spanning 50 million lines — work estimated to require their entire team two months — completing it in a single day. The post describes Fable 5 as targeting tasks requiring sustained attention and multi-step reasoning across long contexts, with code migration, financial analysis, and scientific research cited as primary use cases.
A companion model called Mythos 5 shares the same base but is restricted to vetted life science and cybersecurity partners.
On benchmarks, the post reports Fable 5 achieved the highest score among frontier models on FrontierCode (Cognition), took first place on Hebbia financial reasoning, won the Replit vibe coding benchmark while using fewer tokens, and beat Pokémon FireRed using only visual input. A companion model called Mythos 5 shares the same base but is restricted to vetted life science and cybersecurity partners. Three safety classifiers — covering offensive cybersecurity, bio/chem, and model distillation — ship with the model, with a combined trigger rate under 5% of sessions. The API identifier is `claude-fable-5`, priced at $10/M input tokens and $50/M output tokens, with free access across Pro, Max, Team, and Enterprise tiers through June 22nd.
Key facts
- 01Anthropic released Claude Fable 5 on June 9th with no preview period or waitlist
- 02Stripe used Fable 5 to complete a 50-million-line Ruby codebase migration in one day, a task estimated at two months for their full team
- 03Fable 5 sits above Opus in Anthropic's model lineup
- 04Mythos 5 is the same base model but restricted to vetted life science and cybersecurity partners
- 05Three safety classifiers ship with the model (offensive cybersecurity, bio/chem, model distillation), with a trigger rate under 5% of sessions
- 06Pricing: $10/M input tokens, $50/M output tokens; API identifier is `claude-fable-5`
- 07Free access for Pro, Max, Team, and Enterprise users through June 22nd
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