The Short Version
Claude Fable 5 is the consumer-safe release of Anthropic's Mythos architecture — the same underlying model the company previously reserved for restricted government and security partners. "Fable" is Mythos with cybersecurity safeguards left on; Mythos 5 is the identical model with those guardrails removed for authorized users only (Project Glasswing — US government cyber defenders and infrastructure providers).
The headline: on nearly every published benchmark of raw capability, Fable 5 is the strongest model anyone outside a lab had ever been able to call via an API. It didn't edge out the competition — it cleared it by double digits on coding.
Benchmarks: How Fable 5 Compares
The numbers below are the published launch benchmarks. The coding gap is the story — an 80.3% on SWE-bench Pro is roughly 11 points above the next-best generally available model (Opus 4.8 at 69.2%) and more than 20 points above GPT-5.5 and Gemini 3.1 Pro.
| Benchmark | Fable 5 | Opus 4.8 | GPT-5.5 | Gemini 3.1 Pro |
|---|---|---|---|---|
| SWE-bench Pro (coding) | 80.3% | 69.2% | 58.6% | 54.2% |
| Core analytics (long-running) | 90%+ | ~80% | — | — |
| GDP.pdf (vision/document) | 29.8% | 22.5% | 24.9% | 16.7% |
| Hebbia Finance (senior reasoning) | Highest of any model | — | — | — |
A few things worth flagging about these numbers. The vision/document scores look low across the board because GDP.pdf is a deliberately brutal benchmark — dense, real-world financial PDFs. Fable still leads it. And the finance and analytics gains aren't toy-benchmark wins: they map directly onto the kind of multi-step, document-grounded reasoning that real knowledge work depends on.
What's Actually New
Pricing: The Catch
Fable 5 is not cheap. At launch it was priced at $10 per million input tokens and $50 per million output tokens — double Opus 4.8's rates ($5 / $25).
| Model | Input / 1M | Output / 1M |
|---|---|---|
| Claude Fable 5 | $10 | $50 |
| Claude Opus 4.8 | $5 | $25 |
| GPT-5.5 | $5 | $30 |
The economic argument for Fable was never per-token price — it was tasks completed per dollar. If one model finishes a two-month migration in a day on the first try, the headline rate stops mattering. But for high-volume, simple workloads, the routing fallback to Opus and the 2× price made Opus 4.8 the saner default for most teams anyway.
Should You Build on Fable 5?
Assuming access returns, the decision is straightforward:
- Use Fable 5 for: large-scale code migrations, long-horizon agentic tasks, deep financial/document analysis, anything where a single correct first-pass on a hard problem is worth a premium.
- Stick with Opus 4.8 for: general coding, day-to-day chat, high-volume pipelines, and any workload where the 2× price and occasional safety-reroute aren't worth it.
- Reach for GPT-5.5 for: creative writing and a warm, natural conversational tone, where it still leads.
- Reach for Gemini 3.1 Pro for: the hardest reasoning benchmarks and price-sensitive frontier work.
For a full side-by-side of the entire June 2026 lineup — not just Fable — see our best AI models right now breakdown, or jump straight to the interactive AI Model Selector and benchmark explorer.
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