The most common question from developers who start paying for Claude Max or Claude Pro is always the same: do I actually need Opus, or is Sonnet good enough?
It's not a simple answer. Both models are built on the same architecture. Both write real code. But they make different tradeoffs — and the difference only becomes obvious when you've used both for the same type of work.
The Quick Answer
Use Sonnet 4.6 for 80–90% of your coding work. It's faster, it costs less, and it handles the vast majority of tasks without any quality difference you'd notice.
Use Opus 4.6 when you're doing something that requires sustained multi-step reasoning: untangling a complex bug across many files, designing a system from scratch, or reviewing an architecture where the wrong call has large downstream consequences.
The rule that works in practice: start every session in Sonnet and switch to Opus when Sonnet gets it wrong twice in a row on the same problem.
Speed and Cost — The Practical Reality
Sonnet 4.6 generates tokens roughly 2–3x faster than Opus 4.6. On a complex refactor producing 800 lines of output, that's the difference between a 25-second response and a 60-second one. For iterative work, that multiplies across dozens of interactions.
On Claude Max (subscription plan), you still hit usage limits faster with Opus — each request consumes more capacity. Opus is a finite resource even on Max. Use it deliberately, not by default.
Where Sonnet 4.6 Is Genuinely Better
Boilerplate and scaffolding
// Sonnet generates this just as well as Opus
export async function createUser(data: CreateUserDto): Promise<User> {
const existing = await db.user.findUnique({ where: { email: data.email } })
if (existing) throw new ConflictException('Email already in use')
const hashed = await bcrypt.hash(data.password, 12)
return db.user.create({
data: { ...data, password: hashed },
select: { id: true, email: true, name: true, createdAt: true }
})
}
Generating endpoints, CRUD handlers, components, test files — Sonnet handles all of this at the same quality as Opus. No reason to spend Opus credits here.
Also Sonnet-territory:
- Refactoring with clear requirements
- Writing tests for known behavior
- Debugging well-isolated bugs
- Documentation and code review
Where Opus 4.6 Earns Its Cost
Multi-file bugs with indirect causation
The hardest bugs are the ones where the symptom is three layers away from the cause. A user sees a blank screen. The issue is a race condition between an auth token refresh and a cached API response, which causes a stale closure to capture an undefined value that gets used in a render function.
Sonnet finds the symptom. Opus works backwards to the root cause, traces the full call chain, and fixes the right thing. This is where the reasoning difference is most visible.
Architecture and system design
"Should we use Redis pub/sub or a message queue here?" "How should we structure tenant isolation?" These questions have tradeoffs that compound. Opus holds more context simultaneously and reasons through second-order consequences — it catches the "yes but if you do that, then X breaks because Y" that Sonnet misses on complex design questions.
Security review
Identifying SQL injection vectors, SSRF possibilities, JWT validation errors — security reasoning requires thinking adversarially and tracking subtle data flows. Opus is noticeably better at this. Use Opus for security passes before releases.
The Model Selection Workflow in Claude Code
# Start in Sonnet (default, fastest)
claude
# Realize the bug is more complex than expected — switch:
# /model claude-opus-4-6
# Or set Opus as default for sessions where you know it's needed:
claude --model claude-opus-4-6
The pattern that works:
- Start in Sonnet for every new task
- If Sonnet gets it wrong, switch to Opus for that specific problem
- Once Opus resolves the hard part, switch back to Sonnet for implementation
Use Opus as a specialist you bring in for hard problems — not a general assistant you leave running all day.
Task-by-Task Decision Guide
| Task | Use |
|---|---|
| Writing new endpoints / components | Sonnet |
| Refactoring with clear spec | Sonnet |
| Writing tests | Sonnet |
| Documentation and comments | Sonnet |
| Well-isolated bug fix | Sonnet |
| Multi-file bug with unclear root cause | Opus |
| System architecture decisions | Opus |
| Security review | Opus |
| Debugging unfamiliar library | Opus |
| Large codebase refactor (20+ files) | Opus |
The Real Difference Is Problem Type, Not Problem Size
Common mistake: thinking "big task = Opus, small task = Sonnet". That's wrong.
The correct frame is problem type:
- Well-defined transformation → Sonnet (even if it touches 50 files)
- Open-ended reasoning with non-obvious solution → Opus (even if it's one function)
A large refactor where you've already figured out the approach is a Sonnet task. A single function that keeps returning the wrong result and you can't figure out why is an Opus task.
Sonnet 4.6 is the right default. It's not a compromise — it handles most coding work correctly and returns answers fast enough to keep the iteration loop tight. Opus 4.6 is a specialist: bring it in for the problems that genuinely require it, and you'll notice the difference immediately.
Full article at stacknotice.com/blog/claude-sonnet-vs-opus-coding-2026
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