Claude Fable 5 vs GPT-5.5 vs Gemini 3.1 Pro
Anthropic just released Claude Fable 5 — its first Mythos-class model available to the public. It's already #1 on Hacker News with 1800+ points. Here's how it compares to GPT-5.5 and Gemini 3.1 Pro on every benchmark that matters.
📋 Table of Contents
Quick Comparison Table #1 — Claude Fable 5 (Anthropic) #2 — GPT-5.5 (OpenAI) #3 — Gemini 3.1 Pro (Google) Head-to-Head Benchmarks Final Verdict — Which Should You Use? FAQQuick Comparison
| Feature | Claude Fable 5 | GPT-5.5 | Gemini 3.1 Pro |
|---|---|---|---|
| Release Date | June 9, 2026 | March 2026 | April 2026 |
| SWE-bench Pro | 80.3% | 58.6% | 54.2% |
| SWE-bench Verified | 95.0% | 78.2% | 72.1% |
| GDPval-AA (Elo) | 1932 | 1769 | 1314 |
| Input Price (/1M tokens) | $10.00 | $5.00 | $3.50 |
| Output Price (/1M tokens) | $50.00 | $25.00 | $14.00 |
| Context Window | 200K | 256K | 2M |
| Safety Guardrails | Fable (safe) + Mythos (restricted) | Standard | Standard |
| Best For | Coding, reasoning, knowledge work | General use, cost efficiency | Long context, multimodal |
Claude Fable 5 is Anthropic's first public Mythos-class model. Released on June 9, 2026, it represents a significant leap over Claude Opus 4.8, with 10%+ improvement across all major benchmarks. The model comes in two configurations: Fable 5 (public, with safety guardrails) and Mythos 5 (restricted access, no guardrails). Fable 5 blocks responses in high-risk domains like cybersecurity and biology, while Mythos 5 is available only to vetted researchers and government entities. Pricing is $10/$50 per million input/output tokens — premium, but justified by the performance gap.
Pros
- Best-in-class coding performance (80.3% SWE-bench Pro)
- Strongest knowledge work scores (1932 Elo GDPval-AA)
- Excellent tool use and function calling
- Dual safety model (Fable + Mythos)
- 30-day data retention for API users
Cons
- Most expensive of the three models
- Smaller context window than Gemini (200K vs 2M)
- Safety guardrails may block some legitimate use cases
- Rate limits may apply during initial launch period
GPT-5.5 remains OpenAI's flagship model and the most widely integrated AI in the market. While it falls behind Claude Fable 5 on coding and knowledge work benchmarks, it offers a compelling value proposition at roughly half the price. The OpenAI ecosystem — including ChatGPT, API, Codex, plugins, and GPT Store — gives it unmatched reach. For teams already invested in the OpenAI stack, switching costs may outweigh the benchmark gap.
Pros
- Half the price of Claude Fable 5
- Largest ecosystem (ChatGPT, plugins, GPT Store)
- Better context window (256K)
- Codex integration for coding tasks
- Most third-party integrations
Cons
- Lags significantly on coding benchmarks
- Lower knowledge work scores
- No equivalent to Mythos unrestricted mode
- Data retention policies less clear
Gemini 3.1 Pro is Google's latest frontier model, and while it trails on pure coding benchmarks, it offers the largest context window in the industry at 2 million tokens — 10x Claude Fable 5's 200K. This makes it uniquely suited for tasks that require processing massive documents, codebases, or datasets in a single prompt. It's also the cheapest of the three at $3.50/$14 per million tokens, making it the best value for high-volume, context-heavy workloads.
Pros
- Massive 2M token context window
- Cheapest of all three models
- Strong multimodal capabilities
- Deep Google ecosystem integration
- Free tier available in AI Studio
Cons
- Weakest coding performance of the three
- Lower knowledge work scores
- Smaller developer community
- Fewer third-party integrations
📊 Head-to-Head Benchmarks
All benchmark data sourced from Anthropic's published tables, independent evaluations by LLM-stats.com and BenchLM.ai, and the Artificial Analysis GDPval-AA leaderboard. Scores as of June 10, 2026.
| Benchmark | Claude Fable 5 | GPT-5.5 | Gemini 3.1 Pro | Winner |
|---|---|---|---|---|
| SWE-bench Verified | 95.0% | 78.2% | 72.1% | Fable 5 |
| SWE-bench Pro | 80.3% | 58.6% | 54.2% | Fable 5 |
| GDPval-AA (Elo) | 1932 | 1769 | 1314 | Fable 5 |
| OSWorld-Verified | 83.4% | 71.2% | 68.9% | Fable 5 |
| Tool Use (BFCL) | 91.2% | 86.7% | 79.3% | Fable 5 |
| MMLU-Pro | 89.1% | 86.4% | 84.7% | Fable 5 |
| Context Window | 200K | 256K | 2M | Gemini |
| Input Cost (/1M) | $10.00 | $5.00 | $3.50 | Gemini |
| Output Cost (/1M) | $50.00 | $25.00 | $14.00 | Gemini |
🛠️ Best Tools to Use With These Models
Get the most out of these frontier models with the right tools and platforms.
Access Claude Fable 5 directly through the Claude web app. The $20/month Pro plan gives you generous usage of Fable 5, while the $100/month Max plan unlocks near-unlimited access. Best for anyone who wants the most capable AI for coding and complex reasoning.
Cursor is an AI-native code editor that supports Claude Fable 5, GPT-5.5, and Gemini models. Switch between models based on your task. Use Fable 5 for complex refactors, GPT-5.5 for quick edits, and Gemini for long-context file analysis.
OpenAI's ChatGPT Plus gives you GPT-5.5 access with the broadest ecosystem of plugins, GPTs, and integrations. Best for general-purpose AI use, content creation, and anyone already in the OpenAI ecosystem.
🏆 Final Verdict
For coding and complex reasoning: Claude Fable 5 is the clear winner. It outperforms GPT-5.5 by 20+ percentage points on SWE-bench Pro and dominates knowledge work benchmarks. If you're a developer or researcher, this is the model to use.
For cost-sensitive work: GPT-5.5 at half the price is the sweet spot. It's not as capable on hard tasks, but it's good enough for 90% of everyday AI use cases.
For long-context tasks: Gemini 3.1 Pro's 2M token context window is unmatched. If you need to process entire codebases, legal documents, or massive datasets in a single prompt, nothing else comes close.
Our recommendation: Use multiple models. Many developers use Claude Fable 5 for complex work, GPT-5.5 for everyday tasks, and Gemini for long-context analysis. The best AI strategy in 2026 is model-agnostic.
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