The Myth Goes Public: Fable 5 Release Day
Anthropic · Released June 9, 2026
The myth
goes public.
Claude Fable 5 is the first Mythos-class model anyone can use: the most capable AI Anthropic has ever released to the public, told with guardrails so the whole world can hear it.
Chapter I · The Myth
First came Mythos, and it stayed behind closed doors.
In April 2026, Anthropic unveiled Claude Mythos, a line of extremely large frontier models. It was not released to the public. The reason: Mythos proved remarkably good at finding and exploiting software vulnerabilities, capabilities too dangerous to hand out broadly.
Instead, access went to trusted defenders. Through Project Glasswing, cybersecurity partners used Mythos Preview to uncover thousands of critical vulnerabilities across major operating systems and browsers, hardening software before attackers could strike.
April 2026
Claude Mythos
The unrestricted frontier model. Reserved for approved organizations and Project Glasswing defenders. Today, partners upgrade to Mythos 5.
Trusted access onlyJune 9, 2026
Claude Fable 5
The same Mythos-class power, retold for everyone, with safeguards that block its sharpest edges. The first model in the Claude 5 family.
Generally availableChapter II · The Power
The longer the task, the larger the lead.
Anthropic says Fable 5 is state of the art on nearly every tested benchmark: software engineering, knowledge work, vision, and scientific research. Its defining trait is endurance. It plans an approach, checks progress against the goal, and refines as it goes.
10%+
Beyond Opus 4.8
On some benchmarks, Fable 5 scores more than ten percent higher than Claude Opus 4.8, itself released just weeks earlier.
Days
Of autonomous work
In agent harnesses like Claude Code, Fable 5 can sustain complex multi-step work for days at a time, longer than any prior Claude.
90%
Core analytics benchmark
The first model to break ninety percent on Anthropic's benchmark of long-running analytical tasks, a ten-point jump over Opus. Also the strongest finance-focused model they have tested.
Chapter III · The Gate
How a myth becomes safe to tell.
Releasing this much capability required new safeguards. Classifiers watch for high-risk territory: cybersecurity, chemistry, and biology. When a request crosses into those domains, Fable 5 steps back and Claude Opus 4.8 answers instead. Anthropic expects the gate to trigger in fewer than five percent of sessions.
95%+ of sessions
full Mythos-class capability
High-risk domains
answered safely instead
Chapter IV · The Window
Two weeks before the toll begins.
Compute for a model this large is scarce, so access comes in phases. Right now Fable 5 is included in Pro, Max, Team, and seat-based Enterprise plans at no extra cost. That changes soon.
13
Days left in the included-access window, counting today
Epilogue · The Moral
Every fable carries the power of the myth it came from. The difference is that a fable is told so everyone can learn from it safely.
Why Anthropic named it Fable
