Claude Fable 5 (Mythos) Is Live — Anthropic's Mythos-Class Frontier Model

June 10, 2026

Update — June 13, 2026: Claude Fable 5 (Mythos) has been pulled back after a DoW notification and is no longer selectable. See Kimi K2.7 Code Is Live, Fable 5 Pulled Back for the current availability note.

Claude Fable 5 (Mythos) is in the model picker today. It's Anthropic's most capable generally available model — adaptive thinking, a 1M-token context window, and the highest quality rating of any model Alfrada offers, above Claude Opus 4.8. It sits in a new Overkill pricing band above SOTA, for the work where you want the strongest model available and nothing else will do.

What you can do

• Pick Claude Fable 5 from the model selector on any plan — it's a deliberate, manual pick. The Auto router will never route you to it.
• The hardest reasoning — multi-constraint strategy problems, adversarial analysis, proofs and arguments that have to hold up under scrutiny. This is the model you reach for when a SOTA-tier answer wasn't good enough.
• Long-horizon agentic work — multi-step projects across many tool calls and many turns, where the model needs to keep its plan and its earlier decisions coherent over hours of work.
• Frontier coding — large refactors, subtle concurrency bugs, architecture reviews across a whole codebase in one pass.
• Adaptive thinking — it decides how deeply to reason per request. Simple questions come back fast; hard ones get a long, careful pass. No knob to set.
• 1M-token context window, 128K output — a full data room, a long research corpus, or an entire codebase fits in a single pass, with room left to produce a long deliverable.

Where this shows up

• You ran the analysis with Opus 4.8 and the answer was good but not airtight. You want one more pass from the strongest model available before the decision goes to the board. Fable 5 is that pass.
• You're working a problem that spans an enormous corpus — diligence on a data room, a litigation file, a year of research notes — and you need one model to hold all of it at once and reason across it.
• You're doing frontier-grade coding work where the cost of a wrong answer dwarfs the cost of the tokens.

Try it

• "Here's our market-entry analysis. Steelman the case against it, then tell me where it actually breaks."
• "Hold this entire data room in context and reconcile the inconsistencies between the financials and the management narrative."
• "Review this codebase end to end and find the architectural decisions that will hurt us at 10x scale."

Heads up

• New Overkill band — 24× tokens. Fable 5 is priced at twice the SOTA band: 24 tokens from your free quota per token used, versus 12× for GPT-5.5 and Opus 4.8. Reach for it deliberately, not by default.
• No Zero Data Retention — that's why it's marked [Not Private]. Anthropic does not allow ZDR on Mythos-class models. That means your prompts and outputs are retained on Anthropic's side and could be read by Anthropic personnel — for example during safety reviews. This is different from every other model on Alfrada. We've appended [Not Private] to its name in the picker so you go in with your eyes open: don't send it client-confidential material, personal data, or anything you couldn't afford a third party to see.
• Removed from Auto routing for the same reason. The Auto router will never silently send your work to Fable 5 — using a no-ZDR model must always be your explicit, deliberate choice. It's also not swarm-eligible.
• EU-only geofencing supported. When your work requires EU data residency, Fable 5 requests can be pinned to EU-hosted infrastructure so prompts and outputs stay in-region.
• Available on every package — from Community up through Pro Max, Black, and the VIP tiers.