# Fable 5 and Mythos 5 Share a Model but Separate Access Rules

Times of AI Desk · 2026-06-09 · Models

[https://timesof.ai/2026/06/anthropic-claude-fable-5-mythos-5-launch](https://timesof.ai/2026/06/anthropic-claude-fable-5-mythos-5-launch)

> Anthropic launched Fable 5 for general use with Opus 4.8 fallback and Mythos 5 for restricted partners at $10/$50 per million tokens. AA reported a 64.9 launch index lead using max effort and fallback, which affected about 8% of its tasks.

Anthropic launched **Claude Fable 5 and Claude Mythos 5 on June 9** as two access configurations of the same underlying model. Fable was offered for general use with classifiers and fallback routing; Mythos was restricted to vetted users with specified safeguards lifted. Both launched at **$10/$50 per million input/output tokens**.

## Safeguards and access

Fable routes flagged cybersecurity, biology/chemistry and distillation-related requests to **Claude Opus 4.8**. Anthropic said fewer than 5% of sessions triggered fallback in early data and acknowledged benign false positives. Business traffic on Mythos-class models required **30-day retention for safety**, with the company saying it would not use that data for training.

Mythos 5 initially upgraded existing Glasswing access with cyber safeguards lifted. A separate biology program was planned with biology/chemistry safeguards removed while retaining cyber controls. This was not unrestricted public access.

The launch offered Fable through the API and consumption-based Enterprise. Pro, Max, Team and seat-based Enterprise subscriptions included it through June 22, with usage credits planned afterward unless capacity allowed an extension.

## Claims vs checks

Anthropic described gains in coding, knowledge work, vision and science. Its customer anecdotes and alignment assessments remain vendor-presented evidence.

**Artificial Analysis**, using **adaptive reasoning at max effort with Opus 4.8 fallback**, reported a **64.9 Intelligence Index score, first place**, and **1932 GDPval-AA Elo**. The configuration matters: AA observed fallback on approximately **8% of index tasks**, versus Anthropic’s under-5% session statistic; the units and workloads differ. Its separate GDPval-AA report recorded **2% task fallback**.

## Limits

These are launch terms and dated evaluation results, not current availability. Fallback means some measured work was answered by another model. No later Arena placement or export-control timeline is established by this launch brief.

**Correction (October 14, 2026):** Added AA’s evaluation effort and measured fallback rates; removed unverified retrospective Arena rankings and export-control chronology from the launch account.

## Sources

- [Anthropic: Fable 5 and Mythos 5 launch (June 9, 2026)](https://anthropic.com/news/claude-fable-5-mythos-5)
- [Artificial Analysis: Intelligence Index launch evaluation (June 9, 2026)](https://artificialanalysis.ai/articles/claude-fable-5-mythos-intelligence-index)
- [Artificial Analysis: GDPval-AA evaluation (June 9, 2026)](https://artificialanalysis.ai/articles/claude-fable-5-mythos)