Claude Fable 5: The Most Powerful AI Model on Earth 🛠️

On June 9, 2026, Anthropic released Claude Fable 5. It is a Mythos-class model, the same tier they originally built for government and defense partners. Mythos was considered too powerful to release publicly, so Anthropic added safety classifiers and guardrails, then shipped it under the name Fable.

Fable 5 sits above the Opus class in capability. On the coding benchmarks that actually matter, it beats every other publicly available model by double-digit margins. Stripe used it to complete a 50-million-line codebase migration in a single day that would have taken a team over two months.

The catch: it is expensive. Fable 5 costs $10 per million input tokens and $50 per million output tokens, roughly double what Opus 4.8 costs. It also burns through tokens fast because it thinks longer and harder than any previous model. For most everyday tasks, the older models are still the right choice. But when you need something done that no other model can handle, Fable 5 is in a class of its own.

• SWE-Bench Pro: Fable 5 80.3%, Opus 4.8 69.2%, GPT-5.5 58.6%, Gemini 3.1 Pro 54.2%
• FrontierCode Diamond: Fable 5 29.3%, Opus 4.8 13.4%
• Knowledge and Reasoning: Fable 5 1932, GPT-5.5 1769, Gemini 3.1 Pro 1314
• GPQA Diamond: Gemini 3.1 Pro 94.3%, GPT-5.5 92.8%, Fable 5 91.3%
• Price (input / output per million tokens): Fable 5 $10 / $50, GPT-5.5 $5 / $30, Opus 4.8 $5 / $25, Gemini 3.1 Pro $2 / $12

Fable 5 leads on coding and multi-step engineering work. Gemini 3.1 Pro edges it out on graduate-level science. GPT-5.5 is competitive on reasoning but falls behind on code. If you are building something complex, Fable 5 is the best model available right now.

Within 24 hours of launch, X was flooded with demos. Some were real, some were people repackaging old videos to ride the hype. Here are the verified ones.

Minecraft clone in 20 minutes. A developer gave Fable 5 a single prompt: "Create a clone of Minecraft." Twenty minutes later, it generated a playable version with multiple biomes, a day/night cycle, ores, a cave system, and crafting. About 3,000 lines of code, $12 in API costs.

Boeing 747 from one prompt. Someone used Claude Code with Fable 5 to build a procedural Boeing 747 in Three.js from a single /goal prompt. The agent built the model, set up a headless screenshot camera, and iterated in a vision self-verification loop until it looked right. About 30 minutes.

Solar system physics simulation. Fable 5 built a solar system simulation that derived planetary orbital motion from physics first principles and used it to predict actual solar eclipses. Not a canned animation. Real physics.

Pokemon FireRed beaten with vision only. Anthropic showed Fable 5 playing through the entire game using nothing but screenshots. No game data, no maps, no helper tools. Previous Claude models could not do this even with helper frameworks.

Stripe's 50M-line migration. Stripe reported that Fable 5 completed a codebase-wide Ruby migration across 50 million lines of code in a single day. A human team estimated it would take over two months.

Full 3D websites from one prompt. Multiple developers showed Fable 5 generating complete 3D interactive websites from a single prompt description. Real visual hierarchy, working animations, professional design.

Heads up: some viral demos on X were fake. People repackaged old projects or used other tools and claimed it was Fable 5. Verify before you share.

Fable 5 is available now on all paid Claude plans.

1. Open Claude. Go to claude.com or open the Claude desktop app. You need a paid plan (Pro, Max, Team, or Enterprise).
2. Open the model selector at the top of the conversation.
3. Select Fable 5. Your conversation will now use Fable 5 for responses.

For API access, use the model ID claude-fable-5 at $10 per million input tokens and $50 per million output tokens.

Tip: Fable 5 burns through tokens fast, especially at higher effort levels. For quick questions, casual conversations, or simple tasks, stick with Sonnet or Opus. Save Fable 5 for the hard stuff.

Effort is the biggest dial you have for controlling Fable 5. It determines how long the model thinks before responding.

• Low (0 to 2,000 thinking tokens): summaries, formatting, simple Q and A, classification.
• Medium (2,000 to 8,000): multi-step analysis, code review, structured reports.
• High (8,000+, default): complex reasoning, novel problems, adversarial tasks.
• xHigh (extended): the hardest research and capability-sensitive work.

Fable 5 at medium effort often outperforms older models at their highest settings. Start at High and only go higher when the task demands it. Running everything at xHigh is the fastest way to drain your tokens.

Anthropic published a 14-section prompting guide specifically for Fable 5. The biggest takeaway: everything you learned about prompting other models might actually hurt you here.