Which One Is Claude? Telling the Models Apart

Which One Is Claude?

If you've searched "which one is Claude," you've probably run into a list of names — Claude Opus, Claude Sonnet, Claude Haiku, maybe version numbers like 3.5 or 4 — and you're not sure which one is actually "Claude" versus a variant of it. The short answer: they're all Claude. Claude is Anthropic's family of AI models, and Opus, Sonnet, and Haiku are different sizes within that family, each with a different balance of intelligence, speed, and cost.

Think of it the way you'd think of a car lineup from one manufacturer. A compact, a sedan, and an SUV are all "the brand" — they just serve different needs. Claude works the same way: one company, one underlying architecture philosophy, multiple model sizes released and updated over time.

The Three Model Sizes

Anthropic organizes Claude models into three tiers, and understanding what each is for clears up most of the confusion:

• Claude Opus — the largest and most capable model. Best for complex reasoning, long documents, nuanced writing, and hard coding problems. Slower and more expensive per token.
• Claude Sonnet — the balanced middle option. Strong reasoning and coding ability at a fraction of Opus's latency and cost. This is the default choice for most production apps.
• Claude Haiku — the smallest and fastest model. Built for high-volume, low-latency tasks like classification, extraction, or simple chat replies where speed matters more than depth.

All three are "Claude." None of them is more "real" than the others — they're just optimized for different tradeoffs between quality, speed, and price.

Version Numbers Add a Second Layer

On top of the size tiers, Anthropic ships version updates — you'll see names like Claude 3, Claude 3.5, and Claude 4 generations. Each new version generally improves reasoning, coding accuracy, and instruction-following compared to the previous one, sometimes enough that a newer Sonnet outperforms an older Opus on certain benchmarks.

This is where a lot of the "which one is Claude" confusion comes from: you're not just choosing a size, you're also choosing a generation. When people say "Claude" in casual conversation, they usually mean whichever model currently sits behind the free or default option in the app they're using — which changes over time as Anthropic updates it.

How to Actually Pick One

If you're building something rather than just chatting, the decision comes down to three questions:

1. How complex is the task? Multi-step reasoning, long-context analysis, or advanced coding favors Opus. Straightforward Q&A, summarization, or tagging works fine on Sonnet or Haiku.
2. What's your latency budget? Haiku responds fastest, Sonnet is a solid middle ground, Opus takes longer per response.
3. What's your cost per request? Token pricing scales with model size — Haiku is cheapest, Opus is most expensive, Sonnet sits in between.

A common pattern in real applications: use Haiku for routing and simple lookups, Sonnet for the bulk of user-facing conversation, and Opus only for the requests that genuinely need deeper reasoning.

If You're Building on Claude, Not Just Chatting

If you're a developer trying to figure out which Claude model to call from your own code, the model name goes directly into your API request. Here's a generic example of what that request shape looks like:

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Summarize this contract."}]
  }'

Swapping claude-sonnet-4 for claude-opus-4 or claude-haiku-4 in that same request is literally the only change needed to switch model size — the rest of your integration stays identical.

This is also where a tool like SubToAPI becomes useful if you already have Claude access through a subscription rather than a metered API account. SubToAPI turns that access into a standard HTTPS API with application-specific keys (sub_live_...), so you can call whichever Claude model fits your task without setting up separate billing infrastructure. You get streaming, tool use, and usage metadata through one dashboard, and you choose the model per request the same way you would with any Claude-compatible API — see the quickstart and messages docs for the exact request format.

A Quick Decision Table

| Need | Pick | |---|---| | Fastest, cheapest responses | Haiku | | Balanced everyday use, most apps | Sonnet | | Hardest reasoning, longest documents | Opus | | Streaming responses in a chat UI | Any tier — see streaming docs | | Function calling / agent workflows | Sonnet or Opus — see tools docs |

If you're still not sure, start with Sonnet. It's the tier most people mean when they say "Claude" in a general sense, and it handles the majority of real-world tasks without the cost or latency of Opus.

Bottom Line

There isn't one single "Claude" you need to find — there's a family of models under that name, distinguished by size (Opus, Sonnet, Haiku) and by version generation. Which one you should use depends entirely on what you're doing: casual chat and simple tasks lean toward Haiku or Sonnet, while complex reasoning and long-form work lean toward Opus. If you're integrating Claude into a product, check pricing and the docs to match model choice to your actual latency and cost constraints rather than guessing.

FAQ

Is Opus better than Sonnet? Opus is more capable on complex reasoning and long-context tasks, but Sonnet is faster and cheaper, and often close enough in quality for everyday use. "Better" depends on the task, not a fixed ranking.

Which Claude model does the free chat app use by default? It varies and changes as Anthropic updates its lineup, but the default consumer chat experience typically runs on a Sonnet-tier model, with Opus available as an upgrade option in paid plans.

Can I switch between Claude models in my own app? Yes — the model is just a parameter in your API request. You can call Haiku for simple tasks and Opus for harder ones within the same application, including through SubToAPI.