Claude Opus vs Sonnet: Which Model Should You Use?

Every time you open Claude, there's a small menu next to the send button with a model name in it. Most people never touch it. Others switch to the biggest model for everything and then wonder why they hit their limits by lunchtime. Picking between Opus and Sonnet is one of the simplest ways to get better results and use your plan well.

This comparison follows Anthropic's own model documentation and its Academy guide to choosing a model. I've kept to what Anthropic says about each one and added how I'd split everyday business work between them.

What's the difference between Claude Opus and Sonnet?

Anthropic offers a family of models. In its developer documentation, Opus is described as for long-running agentic coding and knowledge work, and Sonnet as the best combination of speed and intelligence. Above Opus sits Fable, the top tier for demanding reasoning, and below Sonnet sits Haiku, the fastest.

In Anthropic's Academy guide for the Claude app, the plain-English version is this: Sonnet is the daily driver for coding, writing and analysis, and Opus is a large reasoning specialist.

Model	What Anthropic says it's for	Speed
Fable	The most demanding reasoning and long, complex projects	Slower
Opus	Complex, multi-step work that needs deep reasoning	Moderate
Sonnet	Everyday coding, writing, analysis and content creation	Fast
Haiku	Quick answers, summaries and high-volume simple tasks	Fastest

Which Claude model should I use by default?

For the Claude app, Anthropic's Academy says if you're not sure which model to pick, start with Sonnet. It's fast, capable and designed for the bulk of everyday work. Anthropic's developer docs suggest Opus as a starting point for most API workloads, but that advice is aimed at developers building with Claude, not at someone drafting emails in the app.

My rule of thumb for business owners: start every chat on Sonnet, and switch up only when the job needs more thinking than Sonnet gives you.

When is Opus worth it?

Opus earns its place when the task is long, layered and easy to get wrong:

• Working through a long contract, report or set of documents and drawing careful conclusions.
• Planning a complex project with many moving parts and dependencies.
• Multi-step analysis where each step depends on the last.
• Agent-style work in Claude Code or Cowork that runs for a long time.

For a typical social post, email, product description or meeting summary, Sonnet is the better pick. You'll get the answer faster and keep more of your allowance for the jobs that need it.

Does Opus use up my limits faster?

Yes. Anthropic's Academy says Opus uses more of your limit, so reserve it for tasks that need it. Its Claude Code help page puts it more bluntly: Opus uses several times more per turn than Sonnet, and Sonnet more than Haiku. If you keep hitting your limits, check which model you're on before anything else. My guide to Claude usage limits covers the other habits that help.

Which plans can use Opus?

According to Claude's plans page, Haiku and Sonnet are available on every plan, including Free. Opus isn't on Free; it's available on Pro, Max, Team and Enterprise. Fable is included on Max and premium Team and Enterprise seats, and available through usage credits on Pro.

On Enterprise, admins can set a default model for the organisation, but users can still choose a different model for any conversation.

How do I switch between Opus and Sonnet?

In the Claude app, the model menu sits next to the send button. Click the model name and choose another. Anthropic says the change applies from the next response, so you can start on Sonnet and switch to Opus mid-chat when the work gets harder.

The same menu controls effort, from low up to max. Higher effort gives more thorough answers but takes longer and uses more of your limit. For most business writing, the default effort is plenty.

Copy this prompt

Before you answer, tell me in one line whether this task needs deep multi-step reasoning or is a straightforward writing job.
Task: [describe it].
Then do the task.

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Opus vs Sonnet for writing

Anthropic lists writing and content creation as a Sonnet strength, and I couldn't find any Anthropic page saying Opus writes better. For writing, what moves the needle is your brief: who it's for, the tone, an example of your own writing and what to avoid. A short example of your own writing does more for the result than a bigger model.

What about Haiku and Fable?

Haiku is Anthropic's fastest model. Its developer docs describe it as for high-volume tasks such as classification, extraction and routing, and the Academy points to it for quick answers and summaries. It's a good choice when you want a fast rewrite or a short summary and don't need much depth.

Fable sits above Opus. Anthropic describes it as for demanding reasoning and long-horizon work, and it's the slowest of the four. For most small businesses it's overkill for daily work, but it can be useful for the biggest projects, such as analysing a year of documents in one go.

Can I use both in the same chat?

Yes. Because the switch applies from the next response, you can draft a plan on Sonnet, switch to Opus for the one step that needs careful reasoning, then switch back. It's a good habit for long working sessions: you get the depth where it counts without spending your allowance on the easy parts.

Opus vs Sonnet for spreadsheets and analysis

Anthropic's model guide lists data analysis among Sonnet's everyday strengths, so a monthly sales sheet, a list of enquiries or a simple forecast is comfortably Sonnet work. Move to Opus when the analysis has several layers, such as comparing many files, testing different scenarios or explaining why numbers moved across a whole year. If you live in spreadsheets, Claude for Excel is worth a look too.

Signs you're on the wrong model

• You hit your limit early in the day. You may be running everyday jobs on Opus.
• Answers feel shallow on complex work. Switch that chat to Opus and ask again.
• You wait a long time for simple replies. Drop to Sonnet or Haiku for quick jobs.
• Results vary wildly. Check the model menu; it may have changed between chats.

A simple split for a small business

• Sonnet: emails, posts, blog drafts, customer replies, summaries, everyday spreadsheets.
• Opus: strategy documents, long research, tricky analysis, complex planning.
• Haiku: quick rewrites, short summaries and simple sorting jobs.

Copy and paste this prompt

I'm on [plan]. Here are the five jobs I use Claude for most: [list].
For each one, suggest Haiku, Sonnet or Opus, with one line explaining why.
Flag any job where I'm likely wasting my usage limit.

Tools that work with Claude Opus and Sonnet

Both models run in the Claude app on web, desktop and mobile, and in Claude Code and Cowork. Microsoft Excel has its own Claude add-in, and Slack, Google Drive and Notion connect for everyday work. If you compare assistants, ChatGPT and Gemini have their own model menus that follow the same idea: a fast everyday model and a slower reasoning one.

If you'd like help setting up Claude for your team, this is how I work with business owners.

Frequently asked questions

Is Claude Opus better than Sonnet?

Opus is better at long, complex reasoning. Sonnet is faster and Anthropic recommends it as the everyday default in the Claude app for writing, analysis and most work.

Which Claude model should I use?

Start with Sonnet. Switch to Opus for long, multi-step reasoning and use Haiku for quick, simple tasks.

Does Claude Opus use more of my limit?

Yes. Anthropic says Opus uses several times more per turn than Sonnet, so reserve it for jobs that need it.

Can I use Opus on the free Claude plan?

No. Claude's plans page lists Haiku and Sonnet on Free, and Opus on Pro, Max, Team and Enterprise.

How do I change the model in Claude?

Click the model name in the menu next to the send button and choose another. The change applies from the next response.