Which Claude Model Should You Actually Use? A Practical Guide to Opus vs Sonnet vs Haiku
Opus costs 5x more than Sonnet. Sonnet scores 79.6% vs Opus's 80.8% on SWE-bench. For most people, the cheaper model is the right call.
Anthropic makes three Claude models, and the naming is confusing enough that most people just default to whatever their subscription includes. That's a mistake in both directions — sometimes you're overpaying for Opus when Sonnet would do, and sometimes you're using Haiku when the task genuinely needs more horsepower.
Let me save you money and frustration with a simple framework.
The Three Models at a Glance
Here's what you actually get with each tier:
That's an 18x price difference from cheapest to most expensive. And here's the thing that the marketing won't tell you: Sonnet 4.6 scores 79.6% on SWE-bench versus Opus's 80.8%. That's a 1.2 percentage point gap for a 5x price increase.
Sonnet is also the default model in Cursor, Claude Code (on Pro plan), and most API integrations. There's a reason for that — it hits the sweet spot of quality, speed, and cost that works for 90% of tasks.
When to Use Each Model
Haiku ($0.80/$4 per 1M tokens): Use for classification, routing, simple Q&A, data extraction from structured documents, and any high-volume API task where speed matters more than nuance. If you're processing thousands of customer support tickets to categorize them, Haiku is your model.
Sonnet ($3/$15 per 1M tokens): This is the default for a reason. Use for coding, writing, analysis, summarization, email drafting, and any task where you'd normally use a chatbot. If you're not sure which model to use, use Sonnet.
Opus ($15/$75 per 1M tokens): Reserve for genuinely hard problems — complex system architecture, multi-step research that requires deep reasoning, expert-level legal or medical analysis, and situations where being wrong has real consequences. If Sonnet gives you a 95% answer and you need 99%, Opus is worth the premium.
The mental model: Haiku is your intern (fast, cheap, handles routine work). Sonnet is your senior colleague (reliable, covers most situations). Opus is the expert consultant (expensive, called in when the stakes are high).