Claude Code Opus vs Sonnet: When to Use Each Model
Opus 4.6 costs 3x more tokens than Sonnet 4.6 per session. But does it produce 3x better code? Here's a practical guide to choosing the right model for every task.
Two Models, Very Different Economics
Claude Code gives you access to multiple models: Opus 4.6 (the flagship), Sonnet 4.6 (the workhorse), and Haiku 4.5 (the lightweight). Most developers default to whatever Claude Code selects automatically — but that default isn't always optimal for your budget.
Here's what the numbers look like in practice:
| Model | Typical Session Tokens | Relative Cost | Speed | Best For |
|---|---|---|---|---|
| Opus 4.6 | 50-150K | 3x | Slower | Complex reasoning |
| Sonnet 4.6 | 30-80K | 1x (baseline) | Fast | Most coding tasks |
| Haiku 4.5 | 10-30K | 0.3x | Fastest | Simple tasks |
The takeaway: Opus burns through your plan allocation roughly 3x faster than Sonnet for a comparable task. On a Pro plan, that's the difference between 15 productive sessions and 5 before hitting rate limits.
When Opus Is Worth the Premium
Opus 4.6 is genuinely better than Sonnet at certain tasks. Use it when:
Multi-File Architecture Changes
When a change requires understanding how 10+ files interact — database models, controllers, services, views, tests — Opus's deeper reasoning produces significantly better results. It's better at maintaining consistency across files and catching edge cases that Sonnet misses.
Complex Debugging
If a bug involves subtle interactions between multiple systems (race conditions, caching issues, auth flows), Opus's extended thinking capability helps it trace the logic more reliably. It's also better at suggesting root cause fixes rather than surface-level patches.
System Design and Planning
When you need Claude to evaluate trade-offs — "should we use event sourcing or a traditional CRUD approach for this feature?" — Opus produces more nuanced, well-reasoned analysis. Its recommendations account for more edge cases and long-term implications.
Unfamiliar Codebases
When you drop Claude into a large, unfamiliar codebase and ask it to understand the architecture, Opus is better at building a correct mental model from the code. It makes fewer incorrect assumptions about how components relate.
When Sonnet Is the Better Choice
For the majority of day-to-day coding tasks, Sonnet 4.6 produces results that are functionally identical to Opus — at 3x lower cost and faster speed.
Writing New Code from Clear Specs
When you know what you want and can describe it clearly — "create a REST endpoint that accepts a JSON payload, validates it, saves to the database, and returns a 201 response" — Sonnet nails it. The task doesn't require deep reasoning, just competent code generation.
Code Reviews and Suggestions
Reviewing code for bugs, style issues, and improvements is pattern-matching work. Sonnet is excellent at this and returns results much faster than Opus.
Writing Tests
Test generation is well-suited to Sonnet. Testing patterns are established, and the task is more about coverage and correctness than creative reasoning. Sonnet generates reliable, comprehensive test suites.
Documentation and Comments
Writing docstrings, README updates, or inline comments doesn't benefit from Opus's reasoning depth. Sonnet's writing quality is excellent for technical documentation.
Repetitive Changes
Renaming a variable across 15 files. Adding a field to every API response. Updating import paths after a refactor. These mechanical tasks are ideal for Sonnet (or even Haiku).
The Haiku Sweet Spot
Don't overlook Haiku 4.5. At roughly 1/10th the cost of Opus, it's perfect for:
- Quick formatting fixes
- Simple one-file edits
- Generating boilerplate code
- Answering quick questions about syntax or APIs
How to Know If You're Using the Right Model
MyTokenTracker's model analytics show you exactly how your usage breaks down across Opus, Sonnet, and Haiku. After a week of tracking, you can see:
- What percentage of sessions use each model
- The average cost per session by model
- Which projects tend to use more Opus vs Sonnet
- Your overall model distribution trend
Most users discover that 20-40% of their Opus sessions could have been Sonnet sessions with no difference in output quality. Making that shift alone can extend your effective plan capacity by 30%.
The Rule of Thumb
Start with Sonnet. Escalate to Opus only when: (1) the task spans multiple files with complex interactions, (2) you need deep architectural reasoning, or (3) Sonnet's first attempt wasn't good enough. This simple rule saves most developers 30-50% of their token budget.