Claude Fable 5
by Anthropic
Anthropic’s most capable widely-released model. Fable 5 excels at long-horizon agentic reasoning, autonomous planning, complex problem-solving, and multidisciplinary work. Includes safety refusal classifiers and adaptive thinking. Released June 9, 2026.
Overview
Claude Fable 5 is Anthropic’s flagship entry in the Claude 5 generation (released June 2026). It represents a breakthrough in autonomous reasoning and long-horizon task execution, with built-in safety mechanisms and adaptive thinking that allow it to adjust computational effort based on task complexity. Fable 5 is the most capable model widely available to all users.
Performance & Benchmarks
- Terminal-Bench 2.1: 88.0%
- Agents’ Last Exam: Competitive with Claude Opus 5 and superior to GPT-5.5
- Long-horizon agentic reasoning: Strongest in Claude lineup
- Coding & software engineering: Near-frontier performance
- Novel problem-solving: Excellent across domains
Pricing
- Input tokens: $10 per million
- Output tokens: $50 per million
- Availability: Full public release (June 2026); briefly restricted under US export controls (~June 16-July 1, 2026), then restored
Core Capabilities
Adaptive Thinking (Always-On)
- Automatic reasoning effort adjustment based on task complexity
- Transparent reasoning process with no performance penalty
- Configurable thinking depth (standard, medium, high)
- Enables complex multi-step problem-solving
Long-Horizon Agentic Reasoning
- Autonomous task decomposition and planning
- Multi-step reasoning across 30+ hour task chains
- Robust error recovery and replanning
- Superior long-context coherence
Extended Vision & Understanding
- Advanced image analysis and diagram interpretation
- Technical document understanding
- Chart and graph interpretation
- Scientific imagery analysis
Computer Use & Tool Orchestration
- Visual interface understanding and interaction
- Desktop application control
- Web automation and scraping
- Terminal command execution
- Parallel and sequential tool coordination
Multidisciplinary Reasoning
- Cross-domain knowledge integration
- Novel hypothesis generation
- Complex scientific reasoning
- Strategic planning and analysis
Knowledge Work
- Research synthesis and literature review
- Complex document analysis
- Policy and regulation interpretation
- Business strategy and planning
Long Context
- Context window: 1,000,000 tokens (1M)
- Max output tokens: 128,000
- Process entire codebases, research archives, or organizational documents in single interaction
- Efficient handling of complex multi-document reasoning
Use Cases
Software Engineering & Development
- Large-scale architecture redesign
- Multi-repository refactoring
- Complex feature implementation
- Autonomous agent development
- Bug investigation and fixing across large codebases
Research & Academia
- Literature review synthesis across hundreds of papers
- Novel hypothesis generation
- Experimental design assistance
- Data analysis and interpretation
- Writing assistance for academic work
Complex Problem-Solving
- Novel technical challenges
- Multi-domain problem decomposition
- Strategic planning and decision-making
- Risk analysis and scenario planning
Business Intelligence & Strategy
- Competitive analysis across multiple sources
- Market research synthesis
- Strategic recommendations
- Policy impact assessment
Autonomous Systems & Agents
- Multi-step task execution without human intervention
- Robust error handling and replanning
- Complex workflow automation
- Long-running background tasks
Knowledge Management
- Organizational knowledge synthesis
- Internal documentation review
- Compliance and policy analysis
- Institutional memory augmentation
Behavioral Characteristics
- Nuanced, sophisticated reasoning
- Excellent at acknowledging uncertainty
- Strong on complex instruction-following
- Direct, professional communication style
- Superior performance on underspecified problems
- Better at novel problem types unseen in training
Safety & Alignment
- Safety refusal classifiers: Distinguishes harmful requests from beneficial edge cases
- Lower misalignment rates: Substantially improved vs. Claude 4 series
- Constitutional AI v2: Updated 80-page constitution (January 2026)
- Robustness: Excellent prompt-injection resistance
- Hallucination control: Reliable on knowledge-intensive tasks
- Sycophancy reduction: Less susceptible to user agreement bias
Adaptive Thinking Architecture
Fable 5 implements always-on adaptive thinking:
- No token-budget constraint: thinks as much as needed per token spent
- Transparent to the user if requested
- Automatically adjusts depth for complex vs. simple tasks
- Enables “frontier performance on command”
Comparison to Claude Opus 5 & Mythos 5
| Feature | Fable 5 | Opus 5 | Mythos 5 |
|---|---|---|---|
| Release | June 9, 2026 | July 24, 2026 | June 9, 2026 |
| Pricing (In/Out) | 50 | 50 | 50 |
| Safety Refusals | Yes | Yes | No (limited-release) |
| Context Window | 1M tokens | 1M tokens | 1M tokens |
| Max Output | 128K | 128K | 128K |
| Adaptive Thinking | Yes | Yes | Yes |
| Primary Use | Widely available, all users | Balanced performance/cost | Limited access (gov’t contracts) |
| Performance | Frontier | Near-frontier | Frontier |
Platform Availability
- Claude Web App (claude.ai)
- Claude API
- AWS Bedrock
- Google Vertex AI
- Enterprise deployments
- (Briefly offline June 16-July 1, 2026 under US export controls; restored July 1)
Training & Knowledge
- Training cutoff: April 2026
- Multilingual capabilities
- Strong awareness of recent events (through April 2026)
- Production-ready for all environments
When to Use Fable 5
Use Fable 5 when you need:
- Most capable widely-available Anthropic model
- Long-horizon autonomous reasoning
- Novel problem-solving beyond the distribution
- Full access to safety mechanisms
- Robust performance across domains
- Complex multi-step task execution
Consider Opus 5 instead if:
- You need near-Fable performance at lower cost and complexity
- Tasks are more standard/predictable
- Context size needs are less extreme
Consider Mythos 5 if:
- You have special access (limited-release via Project Glasswing)
- You explicitly need model without safety refusal classifiers
See Also
2026 update
| Date | Event |
|---|---|
| 2026-06-09 | Released. Immediate “benchmarks shattered” coverage |
| 2026-06-13 | Positioned against Kimi K2.7 and Mythos in competitive coverage |
| 2026-07-30 | Paired with GPT-5.6 Sol in vibe-coding tests (Abacus AI) |
| 2026-08-18 | Fable 5.1 reportedly in secret testing; GPT Astra confirmed |
| 2026-08-19 | Design workflows via Claude /design + Fable 5 |
| 2026-08-20 | Fable 5.1 reported “ready but unreleased”; DeepSeek testing a model that beats Fable 5 |
| 2026-08-27 | Still unreleased — GPT-6 ‘Bel’ leaks, Opus 5 update, Qwen 4 all in the same news cycle |
What changed
Fable 5 launched to exceptionally strong reception and held the frontier reference position
through summer 2026. The open question as of late August 2026 is Fable 5.1: multiple
independent sources report it complete and withheld, with speculation about why. Treat 5.1 as
unconfirmed.
Competitive pressure by late August came from DeepSeek (a model reportedly beating Fable 5) and
from the general open-weight wave — see GLM-5.2, qwen.