Key Takeaways
- Anthropic’s Claude Fable 5 launches at $10 per million input tokens, cutting Mythos Preview pricing by more than 50%.
- Stripe compressed 2+ months of engineering work into 1 day using Fable 5 on a 50-million-line Ruby codebase.
- Fable 5 is free on Pro and Team plans through June 22, after which usage credits will be required by Anthropic.
What Claude Fable 5 Is
Fable 5 is Anthropic’s most capable publicly available model. In Tuesday’s release, the company says it leads on nearly all tested AI benchmarks, with particular strength in software engineering, knowledge work, scientific research, and long-context tasks. Anthropic notes that the longer and more complex a task, the larger Fable 5’s advantage over its earlier models.
Pricing is set at $10 per million input tokens and $50 per million output tokens. That is less than half the cost of Claude Mythos Preview. Developers can access the model through the Claude API using the string claude-fable-5.
Early Testing Results
The numbers from early testers are specific. Stripe reported that Fable 5 compressed months of engineering work into days, completing a codebase-wide migration across a 50-million-line Ruby codebase in a single day. The same task would have required a full engineering team more than two months to finish by hand.
IMC said Fable 5 passed their trading analysis evaluations across factual lookup, conceptual reasoning, root-cause analysis, and expected-value analysis. On Hebbia’s Finance Benchmark for senior-level reasoning, Fable 5 scored highest among all tested models.
On frontier physics research, one partner reported Fable 5 reached nearly the same result as GPT-5.5 after 36 hours, using roughly a third of the reasoning tokens. GPT-5.5 required four days to reach a comparable result.
Vision and Long-Context Gains
Fable 5 completed the video game Pokémon FireRed using only raw game screenshots, with no maps, navigation aids, or additional tools. Earlier Claude models required a more complex helper setup to play the same game.
On memory and long-context tasks, Anthropic said file-based memory improved Fable 5’s performance on the deck-building game Slay the Spire three times more than it improved Opus 4.8 under the same conditions.
Mythos 5 and Cybersecurity
Anthropic also launched Claude Mythos 5, built on the same underlying model as Fable 5 with certain cybersecurity safeguards lifted. Mythos 5 is being deployed through Project Glasswing, a collaboration with the U.S. government, as an upgrade to Claude Mythos Preview. Anthropic describes it as carrying the strongest cybersecurity capabilities of any AI model currently available.
Safeguards and Availability
Fable 5 includes classifiers that redirect requests touching cybersecurity, biology and chemistry, or model distillation to Claude Opus 4.8 rather than refusing outright. Anthropic says more than 95% of sessions trigger no fallback at all.
A new 30-day data retention policy applies to all Mythos-class model traffic. Anthropic says the data will not be used for model training and will be deleted after 30 days in nearly all cases.
Fable 5 is available now on Pro, Max, Team, and Enterprise plans at no extra cost through June 22. On June 23, usage credits will be required. Anthropic said it intends to restore Fable 5 as part of standard subscription plans once capacity allows.
Separately, Anthropic filed confidentially for an initial public offering in recent weeks. OpenAI followed with a similar filing shortly after. Both developments arrived against a backdrop of continued selling pressure on AI, semiconductor, and mega-cap tech stocks on Wall Street.
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