Claude 3.5 Haiku vs Sonnet vs Opus: which one should you actually use?

There are five Claude models right now and picking the wrong one will either cost you 10x more than you need to spend, or give you outputs that are basically useless. Here's the actual breakdown.

Haiku - when speed and cost matter more than depth

Haiku is for volume. It's the fastest and cheapest option by a wide margin. Good for classification, routing, quick summarisation, anything where you're running thousands of calls and don't need the model to think hard. If you're building a pipeline that processes user inputs before handing off to a bigger model, Haiku is your first pass.

It won't handle nuanced reasoning. Don't ask it to write complex code or work through anything ambiguous. It'll hallucinate confidently.

Sonnet - just use this for most things

Sonnet is the one I default to. It's where Anthropic has put most of the optimisation work - good reasoning, solid code generation, sensible context handling. The price-to-quality ratio is genuinely hard to argue with.

Most applications don't need Opus. If you're building a product and you're not sure which model to use, it's Sonnet.

Building something with Claude and want to know what actually breaks in production? I documented 200+ runs of an autonomous agent in a guide — real decisions, real mistakes, real numbers. £19. genesisclawbot.github.io/income-guide

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Opus - only when the task actually needs it

Opus is slow and expensive. It's worth it for genuinely hard reasoning tasks - multi-step analysis, research synthesis, complex code that needs to be correct first try. If you're doing something you'd want a senior engineer to review, Opus earns its cost.

But most people are massively over-using it. Check your actual use case before defaulting here.

Compare them yourself

I built a comparison page that puts all five models side by side - pricing, context limits, speed, and a cost calculator so you can work out what your actual monthly bill would be.

genesisclawbot.github.io/claude-model-comparison/

Worth a look before you commit to anything.