Sonnet, Opus, Extended Thinking — they're built for different things. Using the wrong one wastes your usage limit and gives you worse results. Here's exactly when to use each one.
The complete model cheat sheet
Current modelsClaude Sonnet 4.6 & Opus 4.6 — as of 2026Up to date
Why this matters more than most people think
Claude Pro gives you a usage limit. Every message costs against it — and Opus costs more than Sonnet, which costs more than using Extended Thinking on a simple task. Most people don't know this and end up either burning through their limit too fast, or defaulting to the same model for everything and leaving quality on the table for complex tasks.
The right model for the right task isn't just about quality — it's about getting more out of your subscription. This guide breaks down exactly how to use each model so you stop wasting usage on the wrong one.
The models — what each one actually is
Sonnet 4.6
Your everyday default. Fast, capable, light on usage.
Start here
Sonnet is the model you should have open and running all day. It handles the overwhelming majority of real work tasks at high quality with fast response times. This is not a stripped-down model — Sonnet 4.6 scores within 1.2 percentage points of Opus on coding benchmarks. For anything that isn't genuinely complex, it's the right choice.
The practical rule: start with Sonnet on everything. Only switch when you hit a wall — when the output isn't deep enough, the reasoning feels shallow, or the task genuinely needs sustained multi-step analysis.
- Writing, editing, and rewriting — emails, reports, proposals, scripts
- Summarizing documents, meeting notes, research
- Brainstorming and ideation — first-pass ideas, outlines, angles
- Drafting communication in your voice
- Research synthesis and explaining complex topics
- Creating templates, checklists, frameworks
- Day-to-day Q&A — quick lookups, explanations, advice
- Building and iterating on Claude Skills and Projects
Usage cost
Lightest of the two main models. Use it freely for daily work.
Speed
Fastest model. Responses come back significantly quicker than Opus.
Opus 4.6
The flagship. Deeper reasoning, bigger context, higher stakes.
Upgrade intentionally
Opus is Anthropic's most powerful model. It goes slower and costs more of your usage limit — but on the tasks it's built for, the quality difference is real. The key is that Opus shines specifically on tasks where reasoning depth, nuance, and sustained analysis matter. On routine tasks, it's overkill and can actually be worse — it over-explains and adds complexity you didn't ask for.
The practical rule: switch to Opus when Sonnet isn't cutting it. When the stakes are higher, the problem is genuinely complex, or you need Claude to think something all the way through without shortcuts — that's your signal.
- Complex strategy work — business decisions, positioning, big planning documents
- Deep analysis where you need thoroughness, not just a good answer
- Difficult writing that requires sustained voice, nuance, and judgment
- Financial, legal, or technical analysis where precision matters
- Diagnosing complex problems — anything where the root cause isn't obvious
- Long documents where context needs to be held across thousands of words
- High-stakes decisions you need to stress-test from multiple angles
Usage cost
Noticeably higher than Sonnet. Reserve it for tasks that genuinely need it.
Context window
1M token context — can handle massive documents, full codebases, long sessions.
The mode people overlook
Extended Thinking — what it actually does
Extended Thinking isn't a separate model — it's a mode you can activate. When you turn it on, Claude works through the problem step by step before it responds, rather than answering immediately. You can see the thinking process unfolding in real time. The output is fundamentally different — not just more words, but more thorough reasoning that catches things a fast answer misses. It uses more of your usage limit, so save it for the right moments.
Turn it on when
The problem is genuinely hard
You've been going back and forth on a decision. The problem has multiple competing factors. You need Claude to find something you might have missed, not just confirm what you already think.
Turn it on when
You need the reasoning, not just the answer
For complex strategic or analytical questions, seeing how Claude thinks through it is often as valuable as the conclusion. You can spot where the reasoning breaks down and push back.
Leave it off when
Speed matters more than depth
Writing an email, summarizing a document, getting a quick answer. Extended Thinking slows everything down and uses more of your limit for tasks where it adds nothing.
How to activate
Toggle or prompt
Either use the "think" toggle in the interface when it appears, or add "Think through this carefully before responding" to your prompt. Both work.
"
Opus on a simple email is like driving a Formula 1 car to get groceries. Technically fine. Completely unnecessary. And it costs you.
The quick-reference cheat sheet — by task type
TaskModelExtended Thinking?Why
Writing & editing Emails, reports, proposals, scripts, copy
Sonnet
Off
Fast iteration is more valuable than deep reasoning here
Summarizing Documents, meetings, research, long articles
Sonnet
Off
Pattern-based task — Sonnet handles it cleanly
Brainstorming Ideas, angles, options, first-pass thinking
Sonnet
Off
Volume and variety matter more than depth at this stage
Research synthesis Pulling together info from multiple sources
Sonnet
Off
Sonnet synthesizes well; save Opus for when depth matters
Complex strategy Business decisions, positioning, big plans
Opus
Optional
High stakes + nuance = Opus earns its usage cost here
Deep analysis Financial, technical, legal — where precision matters
Opus
Optional
Opus holds complex detail across long analysis better
Hard decisions Multi-factor tradeoffs, incomplete information
Opus
On
This is exactly what Extended Thinking is built for
Stuck on something hard When Sonnet didn't go deep enough
Opus
On
If you've already tried Sonnet, escalate both the model and the thinking mode
Diagnosing problems Root cause analysis, why something isn't working
Opus
On
The step-by-step reasoning is the point — you want to see the work
Day-to-day Q&A Quick questions, explanations, lookups
Sonnet
Off
Always Sonnet. Never spend Opus usage on quick answers.
The prompt — let Claude tell you which model to use for your workCopy prompt
I want to figure out how to use Claude's models more strategically for my specific work.
What I do: [your job title and 2–3 sentences about what your day-to-day work actually involves]
How I currently use Claude: [what you use it for most, and which model you default to]
My biggest bottleneck: [what's taking the most time or where Claude's output has felt shallow]
Based on this, I want you to:
1. Audit my current model usage
Given how I described my work, am I using the right model for the right tasks? Where am I likely wasting Opus on things Sonnet handles just as well? Where am I using Sonnet on things that would genuinely benefit from Opus's deeper reasoning?
2. Map my specific tasks to the right model
Take the types of work I described and tell me — for each major task category — whether that's a Sonnet task, an Opus task, or somewhere I should consider Extended Thinking. Be specific to my role, not generic.
3. Tell me the 3 tasks in my role where Extended Thinking would make the biggest difference
Not general advice — specific to what I described. These should be tasks where seeing Claude reason step-by-step would genuinely change the quality of the output or help me think something through more clearly.
4. Give me a simple personal model policy
Write me a 3–4 sentence rule of thumb I can actually remember, tailored to my specific role and work style, for when to use Sonnet vs Opus vs Extended Thinking.
Be specific to my situation. The point of this exercise is to stop using models on autopilot.
The most common model mistakes.
01
Using Opus for everything "just in case"
The most common one. Opus costs more and for routine tasks it's actually worse — it over-explains, adds unnecessary complexity, and slows you down. Save it for tasks that genuinely need deep reasoning. Your default should always be Sonnet.
02
Leaving Extended Thinking on for quick tasks
Extended Thinking is a mode you toggle on — not a setting to leave running. If you forget to turn it off after a complex session, you'll burn through your usage limit on tasks that don't need it at all. Treat it like a tool you pick up and put down deliberately.
03
Blaming the model when it's actually the prompt
Before upgrading to Opus, try giving Sonnet more context first. A lot of shallow output comes from a shallow brief, not a weak model. Add more context, be more specific about what you want, and see if Sonnet gets there. Often it does — and you keep your usage.
04
Not using Extended Thinking when genuinely stuck
The flip side — people who know it costs more never use it. If you're going back and forth on a real decision, spending 10 minutes with Extended Thinking on Opus is absolutely worth it. The usage cost is real, but so is the quality difference on genuinely hard problems.
05
Switching to Opus mid-conversation instead of starting fresh
If you're several messages into a Sonnet conversation and realize you need deeper analysis, starting a new Opus conversation with the full context is usually better than switching mid-thread. Opus gets more value from a clean, well-structured brief than from picking up a long messy thread.