Meet the Models: The Engines Behind Claude

Every door we've walked through — the app, the desktop window, the browser extension — has had something humming away behind it, doing the actual thinking. That something is a model. And here's the part most people never realize: there isn't just one. Claude has a whole lineup of them.

Doorways and engines

Picture the difference between a car and its engine. The doorways we've toured — the app, Code, the connectors — are the cars. The model is the engine inside, the bit that supplies the power. ("Model" is just the industry's word for the trained system doing the work.)

Same engine, different cars, is most of what you've seen so far. But you can also, sometimes, choose a different size of engine for the job in front of you. That's the whole idea of this lesson.

The three everyday engines

Most of the time you'll meet one of three, and the easiest way to keep them straight is by size.

Haiku is the scooter — quick, light, perfect for nipping to the shops. When you want a fast answer to a simple question, this is plenty.

Sonnet is the everyday sedan — the all-rounder you'd happily drive most days. A normal stretch of writing, planning, or working through a problem sits right in its wheelhouse.

Opus is the heavy-duty truck — the one you bring out for the big haul. Gnarly, high-stakes work that has to hold together over a long session is where it earns its keep.

Where the metaphor bends: a truck isn't simply "better" than a scooter. For a quick errand the scooter wins — it's faster off the line and costs you less. Same with the engines. Reaching for the most powerful one out of habit can actually be the slower, pricier choice.

Smarter, not just bigger

The powerhouse has a neat trick worth knowing: it sizes up how hard your request is and adjusts on the fly — answering quickly when something's easy, and taking its time to think when something's genuinely tough. So "more powerful" isn't only about brute force. It's about knowing when to slow down.

The frontier tier (and an honest note)

Above those three sits a frontier tier — the most capable engines Claude has, named Fable and Mythos. They're really the same engine under the hood: Mythos is the full-power version, kept to a small set of vetted partners, and Fable is that same engine wrapped in extra safeguards so more people can use it.

Here's the honest part. Right now, public access to that top tier is paused — an outside legal directive led Anthropic to switch it off for everyone while things get sorted out. The everyday three are completely unaffected, and they're what you'll actually be using anyway.

Remember from the very first lesson how Anthropic leans safety-first? The most powerful engines being the most carefully gated is that same instinct, showing up exactly where you'd expect it.

So which one, when?

You rarely have to think about this, but the instinct is handy. Dashing off a quick reply or looking something up? The light, fast engine is more than enough. A regular day of real work? The everyday all-rounder. A hard, important project you need to trust over hours? That's when you reach for the powerhouse.

We've now seen every door, every way Claude stretches into your world, and the engines humming behind all of it. The last step is putting it together: when you sit down with a real task, how do you decide what to actually reach for? That's where we're headed — turning everything from this tour into a simple gut-check you can lean on.