Mythos, Fable 5, Opus, Sonnet, Haiku. If you follow AI news, you’ve probably run into a wall of names without always knowing which is which. Understanding this hierarchy, though, helps you see where the technology is headed, and what it actually means for you.

Let’s untangle it, no jargon, with one thread to follow: the new class of models known as Mythos-tier, and what it means.

Quick answer: Anthropic offers several AI models ranked by capability. Mythos is the newest and most advanced class, built for security-critical work and limited to select partners. Fable 5 is the public release of that class, with guardrails in place. Below that, Opus is the most capable model available to the public, Sonnet is the balanced option, and Haiku is the fastest. The higher you go, the smarter the AI, but also the pricier and more tightly controlled.

1. Why there are several models

Not every task calls for the same tool. Answering an email is nothing like reviewing a hundred-page contract or securing a critical system. That’s why Anthropic offers a range, from fast and affordable to highly capable and demanding. The right choice depends on the task at hand.

2. The new Mythos class

Mythos marks a real leap forward. It’s a noticeably more powerful class of models, state of the art on expert-level tasks like cybersecurity. Its sharpest version isn’t public, for good reason. Its public, safeguarded version is called Fable 5: it keeps the useful power while blocking risky uses.

3. The everyday lineup

Below this top-tier class sit the models most people and businesses actually use day to day.

Opus: the most capable option for the public, well suited to long, difficult tasks.
Sonnet: the best balance of speed and intelligence, built for everyday production use.
Haiku: the fastest and most affordable, made for simple tasks.

4. How to choose for your business

Good news: you don’t need the most powerful model to get real value. For most small and medium businesses, a balanced assistant built into your existing tools is more than enough. The right approach is to start from the task, not the model’s name.

If you’re torn between assistants, our comparison Copilot or ChatGPT for your business is a good place to start.

5. What this hierarchy tells us

More power doesn’t count for much without the right guardrails. That’s the whole point behind splitting Mythos, restricted and cautious, from Fable 5, public and safeguarded. The future of AI isn’t just about more power, it’s about power that’s managed well.

Frequently asked questions

What’s the difference between Mythos and Fable 5?

Mythos is the most advanced version, and it isn’t public, reserved for select partners. Fable 5 is the public release of the same class, with guardrails that block dangerous uses.