Claude Fable 5

Spec

Attribute	Value
Developer	Anthropic
Tier	Mythos-class (first publicly available)
Released	2026-06-09
Announced	2026-06-09
Context window	unknown
Pricing	$10/M input · $50/M output
License	unknown
Safety gating	Yes — <5% of sessions route sensitive queries to Claude Opus 4.8
Availability	Claude.ai, Claude API, AWS Bedrock, GitHub Copilot, Google Cloud Vertex AI
Free period	Pro / Max / Team / seat Enterprise: free through 2026-06-22 (2× usage credits after)

Release Date

June 9, 2026 — the first publicly available Mythos-class model from Anthropic. Fable 5 and Claude Mythos 5 share one underlying model. Fable 5 wraps the model in classifier gates for general availability; Mythos 5 operates with some gates lifted exclusively for approved Project Glasswing partners (cyberdefenders, infrastructure providers, US government).

Status — restored globally (2026-07-01)

Restoration (2026-06-30 / 2026-07-01)

The US Department of Commerce lifted export controls on June 30, 2026 — 19 days after imposing them. Fable 5 was restored to global users on Claude.ai, Claude Code, Claude Cowork, and the API starting July 1, 2026. Conditions of restoration:

• Fable 5 capped at up to 50% of weekly usage limits through July 7; Anthropic extended free access through July 12, then again through July 19, 2026 at 11:59 PM PT (third extension total, announced July 13 just as the July 12 deadline hit). Terms of the July 19 extension: Pro/Max/Team/Enterprise, no extra cost, +50% rate limit boost. After July 19, Fable 5 credits-only at $10/$50 per Mtok. Anthropic states the subscription restriction is temporary pending capacity expansion. (source)
• Anthropic agreed to proactively detect and address security risks, help develop frontier-model standards, and report any malicious activity to the US government
• AWS, Google Cloud, Microsoft Foundry re-enabling access as quickly as possible

Mythos 5 is being restored to a broader set of US organizations (beyond the ~100–150 cleared on June 26). → Anthropic (source) (CNBC) (Forbes)

Suspension (2026-06-12 to 2026-07-01, 19 days)

Three days after launch, on 2026-06-12 the US government issued an export-control directive ordering Anthropic to suspend all access to Fable 5 and Mythos 5 for any foreign national worldwide (including Anthropic's own foreign-national employees). Anthropic disabled both models for all customers to comply. The government cited a claimed jailbreak method (Amazon researchers demonstrating vulnerability identification and exploit-code generation); Anthropic reviewed the demonstration and found only minor, previously-known vulnerabilities, disputing that this warrants recalling a model deployed to hundreds of millions. Reported as the first US export ban on a named AI model. → (source) (statement)

Benchmarks

Benchmark	Fable 5	Opus 4.8	GPT-5.5	Gemini 3.1 Pro
SWE-bench Pro	80.3%	69.2%	58.6%	54.2%
SWE-bench Verified	95.0%	88.6%	—	—
Terminal-Bench 2.1	88.0%	82.7%	83.4%	70.7%
GDPval-AA (reasoning)	1932	1890	1769	1314
FrontierCode Diamond	29.3%	13.4%	5.7%	—
Notable: the FrontierCode Diamond gap over Opus 4.8 (+15.9 pp) and over GPT-5.5 (+23.6 pp) is unusually large — this benchmark targets the hardest real-world unsolved coding problems.

Fable 5 also surpasses Mythos Preview on SWE-bench Pro (80.3% vs 77.8%), suggesting post-training improvements were made between the April preview and the June GA.

(sources), (BenchLM), (MangoMind)

Use Cases

• Long-horizon software engineering — Stripe case study: codebase-wide migration completed in 1 day vs. 2+ months for a full team
• Complex knowledge work: coding, science, vision, research
• Agentic workflows running for longer than any previous Claude model
• General-purpose reasoning on the hardest tasks (FrontierCode Diamond leader)

Safety Architecture

A two-model approach:

1. Default path: Fable 5 handles the query directly
2. Safety gate (< 5% of sessions): sensitive queries are silently routed to Claude Opus 4.8

This design delivers Mythos-class capability for ≥95% of use cases while preventing misuse in the remaining edge cases. It represents a middle path between "fully open" (Mythos Preview would be unsafe) and "fully restricted" (Mythos Preview was withheld entirely).

Cyber Safeguards (2026-07-01, added at restoration)

At the time of global restoration (July 1, 2026), Anthropic deployed a new safety classifier blocking >99% of attempts replicating the specific jailbreak that triggered the June 12 export-control suspension. Broader behavioral guardrails were also extended.

Cyber Jailbreak Severity (CJS) Framework

Anthropic proposed the CJS framework — co-developed with Amazon, Microsoft, Google, and Glasswing partners — as an industry standard for rating AI jailbreak risk. Four axes: capability gain, breadth, ease of weaponization, discoverability. Five severity bands: CJS-0 (Informational) through CJS-4 (Critical). Also launched a HackerOne bug bounty for Fable 5 cyber jailbreaks. → AI-Enabled Cyberattacks (source) (Anthropic)

Compared To

Model	SWE-bench Pro	Tier	Public?
Claude Fable 5	80.3%	Mythos-class (gated)	✅ Yes
Claude Mythos Preview	77.8%	Mythos Preview	🔒 Glasswing only
Claude Opus 4.8	69.2%	Opus	✅ Yes
GPT-5.5	58.6%	—	✅ Yes
Gemini 3.1 Pro	54.2%	—	✅ Yes

Related

• Claude Mythos Preview — the withheld predecessor; Mythos 5 is the Glasswing-restricted successor sharing Fable 5's weights
• Claude Opus 4.8 — previous public frontier (2026-05-28, SWE-bench Pro 69.2%)
• Anthropic
• AI-Enabled Cyberattacks — Glasswing context for Mythos 5

Sources

• Anthropic — Claude Fable 5 and Mythos 5 (source)
• VentureBeat
• CNBC
• The Decoder
• GitHub Copilot Changelog
• AWS Blog