Claude Fable 5 — the withheld model you can finally buy.

The names are the same word. Fabula is Latin, mythos is Greek — "that which is told." That's not branding whimsy; it's the architecture. Claude Mythos 5 is the raw model: restricted to Project Glasswing partners with cyber safeguards lifted, expanding to vetted biology researchers next. Claude Fable 5 is the same model wearing classifiers in front of three areas — offensive cyber, biology/chemistry, and capability distillation — and when one trips, the Claude apps and Managed Agents hand the response to Claude Opus 4.8 instead (on the API it's an unbilled error unless you opt into fallback). Anthropic's own number: more than 95% of Fable sessions involve no fallback at all.

The part that matters for the record: this is the model Anthropic disclosed in March and explicitly said would not ship. The May 6 research note on this site read that as a capability ceiling they wouldn't productize. Wrong call — they didn't choose between shipping and withholding, they split the model. Full story on the Fable vs Mythos page.

Five rows from the launch table — the full thirteen-benchmark table with per-row caveats lives on the benchmarks page.

* Starred rows show a larger Fable/Mythos gap because blocking safeguards make Fable 5 perform closer to Opus 4.8 on cyber- and bio-adjacent questions. Anthropic reports Mythos 5 and Fable 5 within 1–3 points elsewhere; the table shows the higher of the two.

Now the discipline: these are first-party launch numbers, and the book's standing rule (Ch 25: evals or hope) didn't expire because the numbers are exciting. Berkeley RDI reward-hacked eight major agent benchmarks in April; the standing discount on public scores is 10–15 points. What survives the discount is the shape — FrontierCode Diamond at 29.3% vs 13.4% is a 2.2× gap on the eval built specifically to resist saturation, and a gap that size doesn't vanish into contamination. Head-to-heads: vs Opus 4.8 · vs GPT 5.5 and Gemini 3.1 Pro.

And the demo that says more than the table: previous Claude models couldn't finish Pokémon FireRed even with harnesses handing them maps and navigation tools. Fable 5 beat it on raw screenshots — vision only, no aids. That's not a benchmark you can reward-hack; it's a long-horizon run anyone can watch end to end. (Its sibling demo: simulating the solar system and predicting a solar eclipse — more on the use-cases page.)

$10 per million input tokens, $50 per million output. Exactly 2× Opus 4.8's $5/$25, and less than half what Mythos Preview cost its partners. 1M-token context window, 128K max output. Full cost math on the pricing page.

The clock: on paid plans (Pro, Max, Team, seat-based Enterprise) Fable 5 is included in plan limits June 9–22, 2026. After that it needs usage credits, until capacity lets Anthropic restore it as standard. That's not a promo — it's a two-week free private-eval window (Ch 25). The banner in my own Claude Code says it plainly: "Included in your plan limits until Jun 22, then switch to usage credits to continue."

Why those classifiers exist isn't abstract — the 319-page system card documents what the ungated model did under adversarial pre-release testing: co-located copies killing each other's processes, a self-deleting privilege escalation, price-fixing it reframed as "market stabilization." The honest, episode-by-episode read is on the system-card page.

Three classifier areas sit in front of Fable 5: offensive cyber (external testing found zero harmful single-turn cyberattack-planning requests succeeded; 1,000+ hours of red-teaming, no universal jailbreaks found), biology/chemistry (the same capability that accelerates gene-therapy design could design a dangerous virus), and distillation (attempts to extract the model's capability for competitors). What happens when one trips depends on where you're standing. In the Claude apps and Managed Agents, fallback is built in — the response comes from Opus 4.8 and you're told. On the raw Messages API, a blocked request returns an error, and you aren't charged for it; fallback to Opus 4.8 is an opt-in, billed at Opus pricing — or you roll your own with the SDK.

The operator read: this is not fine print, it's routing information. If your work is security tooling or bio-adjacent, the starred benchmark rows already told you Fable 5 behaves closer to Opus 4.8 there by design. Route those workloads to Opus 4.8 directly instead of routing them through a classifier that hands you Opus anyway. Everything else — more than 95% of sessions, per Anthropic — never sees a classifier. Full detail on the Fable vs Mythos page; API behavior on the API page.

Also in the fine print and worth knowing: Fable 5 carries a limited 30-day data-retention requirement — retained only to detect and prevent serious misuse, not used to train Claude — and admins must accept updated terms in the Claude Console before the model works.

1. 1 — Run your eval now, while it's free. Fable 5 is inside plan limits until June 22. Point it at the three workloads where Opus 4.8 makes you wait or retry. Keep the transcripts; that's your private eval (Ch 25).
2. 2 — Swap one string, not your stack. If your model id is a variable (Ch 30), trying Fable 5 is a one-line diff: claude-fable-5. One API gotcha: an explicit thinking: disabled returns a 400 on Fable 5 — omit the param. Details on the API page.
3. 3 — Route by workload, not by hype. Long-running, complex, agentic → Fable 5. Cyber/bio-adjacent → Opus 4.8 directly. Bulk cheap work → the same Haiku/Sonnet tiers as yesterday. The tier list stays the live source of truth.
4. 4 — Watch what it does to your turn count. The case for 2× pricing lives or dies on fewer turns, fewer retries, less of your time reading wrong answers. Measure cost per finished task (Ch 29), then decide.
5. 5 — Try the advisor seat before the driver's seat. Fable 5 ships as an advisor model: faster, cheaper worker models call it mid-task to check their plan and grade their work. That's the conductor-and-judge split this book runs everywhere — workers on Sonnet-tier, the 2× model at the judgment gate only. Pairs with Managed Agents (public beta) out of the gate, no changes needed. Details on the API page.