Claude Fable 5: Anthropic's Most Powerful Public AI Model β Complete Guide 2026
On June 9, 2026, Anthropic released its most powerful publicly accessible AI model: Claude Fable 5. It delivers the same underlying capability as the access-gated Claude Mythos 5 (previously restricted to government cybersecurity partners under Project Glasswing) but wrapped in safety classifiers for general public use.
The headline: it's not just more capable β it costs less than half the Mythos Preview that preceded it. $10 per million input tokens.
Fable 5 vs Mythos 5: What's the Difference?
They are the exact same model under the hood. The only difference is access control:
- Fable 5: Public β safety classifiers monitor three domains: cybersecurity, biology/chemistry, and distillation attempts
- Mythos 5: Restricted to Glasswing partners (government cyber defenders and select biomedical researchers)
When a query triggers a safety classifier, Fable 5 silently routes the request to Claude Opus 4.8 rather than refusing it. Anthropic reports this happens in fewer than 5% of sessions.
Technical Specifications
- Context Window: 1,000,000 tokens (read an entire codebase in one go)
- Max Output: 128,000 tokens
- Pricing: $10 input / $50 output per million tokens
- Model ID:
claude-fable-5 - Availability: Claude API, AWS Bedrock, Vertex AI, Microsoft Foundry
- Inputs: Text + vision (images, charts, screenshots)
- Thinking: Adaptive Thinking (always on β automatic deep reasoning)
- Data Retention: 30-day mandatory (Covered Model classification)
Pricing Comparison
| Model | Input ($/M tokens) | Output ($/M tokens) |
| ------------------ | ------------------ | ------------------- |
| Claude Fable 5 | $10 | $50 |
| Claude Opus 4.8 | $5 | $25 |
| Claude Sonnet 4.6 | $3 | $15 |
| Fable 5 Batch API | $5 | $25 |
Note: Pro, Max, and Team plan subscribers get Fable 5 at no extra cost from launch through June 22. After that it moves to usage credits.
Key Benchmarks
SWE-Bench Pro (Real GitHub Issue Resolution)
- Fable 5: 80.3%
- Opus 4.8: 69.2%
- GPT-5.5: 58.6%
A 22-point lead over GPT-5.5. These are real software engineering problems, not theoretical exercises.
SWE-bench Verified
- Fable 5: 95.0%
- Opus 4.8: 88.6%
FrontierCode Diamond (Long-horizon Coding)
- Fable 5: 29.3%
- Opus 4.8: 13.4%
Fable 5 is more than 2x better on extended coding tasks β the gap grows as complexity increases.
What Makes Fable 5 Different?
1. True Autonomous Coding
Stripe tested Fable 5 on a 50-million-line Ruby codebase and had it run a codebase-wide migration. The model completed the project in one day β work Stripe estimated would take a team two months of manual effort.
Cursor reported Fable 5 opened "a whole class of long-horizon problems that were out of reach for earlier models."
2. Breakthrough Vision
Fable 5 is Anthropic's best vision model. It completed PokΓ©mon FireRed using only raw screenshots β no maps, no state data, no helper tools. It also reconstructs web app source code from screenshots and extracts precise values from scientific charts.
3. Compounding Memory Advantage
In a controlled evaluation using the strategy game Slay the Spire, giving Fable 5 persistent file-based memory improved its performance 3x more than the same improvement for Opus 4.8. Fable 5 reached the final act 3x more often. The longer the task runs, the bigger Fable 5's lead grows.
Fable 5 vs GPT-5.6 Sol: Head to Head
We covered this more extensively in our GPT-5.6 Sol vs Terra vs Luna comparison, but here's the direct face-off:
| Aspect | Claude Fable 5 | GPT-5.6 Sol |
| ---------------- | ------------------------------ | -------------------- |
| SWE-Bench Pro | 80.3% | ~75% |
| Price (output) | $50/M tokens | $30/M tokens |
| Deep reasoning | Stronger on long tasks | Faster execution |
| Vision | Stronger (Pokemon, charts) | Good |
| Multi-agent | Limited | Ultra (4 agents) |
| 30-day retention | Required | Optional |
Bottom line: Fable 5 wins on long-horizon tasks and vision. GPT-5.6 Sol wins on speed, cost, and multi-agent workflows.
When to Use Each Claude Model
Use Fable 5 when:
- Long, complex coding tasks (codebase-wide migrations, refactors)
- Massive document analysis (contracts, research papers, financial reports)
- Complex vision tasks (chart extraction, screenshot-to-code)
- Multi-step research requiring deep reasoning
Use Opus 4.8 when:
- General coding and daily work
- Well-defined, repeatable tasks
- Zero Data Retention required
- Lower cost needed (half the price)
Use Sonnet 4.6 when:
- High-volume tasks (classification, summarization, RAG)
- Fastest response time
- Lowest possible cost
Important Caveats
1. Safety classifier false positives: If your work touches cybersecurity or biology, expect 10-20% of queries to fall back to Opus 4.8. Anthropic acknowledges the bio classifier is deliberately broad and commits to narrowing it β but no timeline given.
2. 30-day data retention: Fable 5 is classified as a "Covered Model" β your data is retained for 30 days. If your organization mandates Zero Data Retention, you cannot use Fable 5. Even on AWS Bedrock, data temporarily leaves the AWS security boundary.
3. Hidden costs: Fable 5 uses a new tokenizer β pre-Opus 4.7 prompts can inflate by up to 35%. Adaptive Thinking generates hidden reasoning tokens that increase your output bill. Always test token counts before migrating.
Frequently Asked Questions
What is the Claude Fable 5 price per million tokens?
$10 per million input tokens and $50 per million output tokens. Batch API halves this to $5/$25.
What is the Claude Fable 5 model ID?
claude-fable-5 β use this in the Messages API.
What's the difference between Claude Fable 5 and Opus 4.8?
Fable 5 leads by 11% on SWE-Bench Pro (80.3% vs 69.2%) but costs 2x ($10/$50 vs $5/$25). Fable 5 has Adaptive Thinking and stronger vision capabilities.
Is Claude Fable 5 better than GPT-5.6 Sol?
On long-horizon coding and complex multi-step tasks, yes. But GPT-5.6 Sol is cheaper, faster, and supports Ultra Mode (4 parallel agents).
Does Fable 5 support Zero Data Retention?
No β it enforces 30-day retention. Use Opus 4.8 if you need ZDR compliance.
Is Fable 5 free on Claude?
Pro, Max, and Team plan subscribers get Fable 5 free from June 9-22. After June 23 it moves to usage credits.
π See our full GPT-5.6 Sol vs Terra vs Luna comparison
π AI Agents in the UAE β Complete Business Guide
How Katbi Can Help
At Katbi Digital Solutions, we track every frontier AI model and deploy the right one for each client's needs. Whether you need an AI WhatsApp bot, a custom AI agent, or a smarter application backend β we pick the right tool for the job.
π± AI WhatsApp Bots β powered by the best model for your use case
π Web & Mobile Apps β with intelligent AI integration
π€ Custom AI Agents β autonomous task execution for your team
π Google Ads & SEO β AI-optimized campaigns
π± Contact us on WhatsApp