Introducing Claude Fable 5

Ashwani Kumar — Wed, 10 Jun 2026 11:03:11 +0000

Introducing Claude Fable 5

Claude Fable 5 is our most capable model yet, now generally available. It’s a Mythos-class model with safeguards that let us share it broadly without compromising on safety.

It can stay with complex tasks and hard problems for days, handling ambitious work across coding, research, analysis, finance, law, and beyond.

Learn more: https://www.anthropic.com/news/claude…

Claude Fable 5, Anthropic’s new “Mythos-class” model, is specifically engineered to handle highly complex, multi-step work that previously required constant human supervision. Its suitability for ambitious projects stems from several key factors:

Long-Horizon Autonomy: The model is designed for persistent, multi-day operations. It can stay with complex problems and operate for days without intervention (1:22 – 1:36), making it ideal for tasks like large-scale code migrations or deep research projects.
Self-Correction and Agentic Capabilities: Fable 5 features built-in verification loops, enabling it to test its own code, self-correct, and manage sub-agents to complete intricate, multi-step projects.
Advanced Reasoning & Coding: It demonstrates superior capability in complex coding, data-driven agentic workflows, and 3D design, allowing it to take on challenging projects across fields like finance, law, and economics.
Vision-Based Analysis: The model can interpret and analyze complex technical figures or screenshots, and even rebuild applications based on visual input.
Enterprise-Grade Safety: While powerful, it includes robust, automatic safeguards. If a request touches on high-risk areas like cyber security or biology, the system is designed to intelligently redirect those specific parts of the request to Opus 4.8, ensuring safety without compromising general productivity (0:52 – 1:13).

Claude Fable 5 is Anthropic’s first generally available “Mythos-class” intelligence model, built specifically for highly autonomous, multi-day engineering and complex knowledge tasks. Released alongside the highly restricted Claude Mythos 5, Fable 5 introduces a new era of AI focused on handling long-horizon responsibilities independently rather than executing isolated, short-term tasks. [1, 2, 3]

Core Model Specifications

Context Window: 1 million tokens default input capacity.
Output Limit: Up to 128,000 output tokens per single request.
Pricing: $10 per million input tokens and $50 per million output tokens.
Adaptive Thinking: Forced natively; “raw” unsummarized thinking content is permanently omitted to protect backend reasoning architecture. [2]

Standout Features & Performance

1. Long-Horizon Autonomy [4]

Fable 5 can plan across distinct operational stages, delegate sub-tasks to smaller parallel sub-agents, and dynamically check its own work over the course of several days without user intervention. In a trial with Stripe, the model migrated a complex 50 million-line Ruby codebase in one day—a process that typically takes humans months. [5, 6, 7, 8]

2. Specialized Domain Benchmarks

According to official reports from Anthropic and early platform testers, Fable 5 sets a new state-of-the-art across complex benchmarks: [9]

SWE-Bench Pro (Coding): Scores 80.3%, decisively beating Claude Opus 4.8 (69.2%) and GPT-5.5 (58.6%).
OfficeQA Pro (Enterprise QA): Achieves 57.9% correctness on multi-modal document search and code execution pipeline tests.
Core Analytics (Finance): Breaks the 90% threshold on long-running analytical filing tasks. [6, 7, 10]

3. Advanced Multimodal Vision [4]

The model interprets dense technical blueprints, complex charts, and financial spreadsheets with higher accuracy than prior generations. It uses standard command-line tools to crop, unblur, or flip incoming source images autonomously. In a showcase of visual capability, Fable 5 successfully played and completed Pokémon FireRed relying purely on raw visual context. [3, 4, 9]

The “Silent Fallback” Safety System

Because Fable 5 shares the raw architecture of Mythos 5—which possesses extreme cybersecurity exploit and biology capabilities—Anthropic built an automated domain-specific fallback system. [2, 7, 11]

How it works: Automated safety classifiers silently evaluate every prompt session.
Rerouting: Queries flagging high-risk vectors (like cyberattack routes or biological weapon synthesis) are automatically routed down to Claude Opus 4.8.
Triggers: This automated redirection happens in fewer than 5% of total sessions on average.
Billing: Users are not charged the premium Fable 5 token rate for any prompt that triggers an Opus 4.8 fallback. [3, 7]

Availability and Access Pathways

Developers and enterprises can immediately leverage claude-fable-5 across major cloud ecosystems, including the Anthropic Claude Platform, Amazon Bedrock, Google Cloud Vertex AI, and Microsoft Foundry. [2]

For standard consumer subscription tiers (Pro, Max, Team, and Enterprise), Fable 5 is included at no extra cost during an initial rollout window extending through June 22, 2026. On June 23, it will be removed from standard tiers and shift to credit-metered access while Anthropic monitors compute capacity. [9]

Introducing Claude Fable 5