Claude Code Sonnet vs Opus (2026)

Quick Verdict

Sonnet 4.6 handles 80% of development tasks at 80% lower cost than Opus 4.6. Use Sonnet as the default model and switch to Opus only for complex architecture decisions, nuanced debugging, and multi-step reasoning tasks. A developer spending $500/month on all-Opus can reduce to $150/month by routing tasks appropriately – with no measurable quality loss on routine work.

Pricing Breakdown

Model Input Cost/MTok Output Cost/MTok 100K Session Cost 500K Session Cost
Sonnet 4.6 $3.00 $15.00 $0.75 $3.75
Opus 4.6 $15.00 $75.00 $3.75 $18.75
Haiku 4.5 $0.80 $4.00 $0.20 $0.98

Opus costs exactly 5x Sonnet for input and 5x for output. The question is whether Opus delivers 5x the value for a given task.

Feature-by-Feature Cost Analysis

Bug Fixes (Single File)

Typical token usage: 20K-35K input, 5K-12K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 30K input / 8K output 25K input / 7K output
Cost per fix $0.21 $0.90
Success rate (first attempt) 85% 92%
Cost including retries $0.25 $0.98

Sonnet is 75% cheaper per bug fix. Opus fixes slightly more bugs on the first attempt, but the retry cost is minimal. Winner: Sonnet – the 7% success rate improvement does not justify the 4x price premium.

Feature Implementation (2-3 Files)

Typical token usage: 60K-120K input, 20K-40K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 90K input / 30K output 75K input / 25K output
Cost per feature $0.72 $3.00
Quality score (code review pass rate) 78% 89%
Rework cost (when needed) $0.36 $1.50
Total cost (including rework) $0.80 $3.17

Sonnet is 75% cheaper per feature. Opus produces higher quality on the first pass, but rework on Sonnet is cheap. Winner: Sonnet for routine features. Opus justified only when the feature requires novel architecture decisions.

Architecture Design

Typical token usage: 100K-200K input, 40K-80K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 150K input / 60K output 120K input / 50K output
Cost per design $1.35 $5.55
Quality score 65% 88%
Rework sessions needed 1.5 avg 0.4 avg
Total cost (including rework) $3.38 $7.77

For architecture work, Opus quality is significantly higher (88% vs 65%). Sonnet requires 1.5 rework sessions on average, each costing $1.35. Winner: Opus – the quality difference justifies the cost for architecture tasks that impact the entire codebase.

Test Writing

Typical token usage: 25K-50K input, 10K-25K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 35K input / 15K output 30K input / 13K output
Cost per test file $0.33 $1.43
Test coverage quality 82% 87%

Winner: Sonnet – the 5% coverage improvement rarely justifies 4.3x cost.

Complex Debugging (Multi-File, Unclear Root Cause)

Typical token usage: 100K-300K input, 30K-80K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 200K input / 50K output 130K input / 35K output
Cost per debug session $1.35 $4.58
Resolution rate 60% 82%
Escalation cost (when unresolved) $1.35 per retry $4.58 per retry
Total cost to resolution $3.38 $5.58

Opus resolves complex bugs 37% more often on the first attempt and uses 35% fewer input tokens (better focus). Winner: Opus for genuinely complex debugging. Sonnet for straightforward debugging.

Refactoring

Typical token usage: 80K-200K input, 30K-60K output.

Metric Sonnet 4.6 Opus 4.6
Average tokens 120K input / 40K output 100K input / 35K output
Cost per refactor $0.96 $4.13
Consistency across files 75% 90%

Winner: Sonnet for small refactors. Opus justified for large-scale pattern changes where consistency matters.

Real-World Monthly Estimates

Light User (~2 hrs/day)

Model Daily Tasks Monthly Cost
All Sonnet 8 tasks $54
All Opus 8 tasks $270
Optimal mix (80/20) 8 tasks $97

Heavy User (~6 hrs/day)

Model Daily Tasks Monthly Cost
All Sonnet 25 tasks $169
All Opus 25 tasks $845
Optimal mix (80/20) 25 tasks $304

Compared to Claude Code Max

Plan Monthly Cost Best For
Max Individual $100 Medium-heavy users (unlimited Sonnet + Opus)
Max Team $200/seat Teams needing both models
API Sonnet only $54-$169 Light users or Sonnet-only workflows
API Optimal mix $97-$304 Users needing precision model control

Break-even for Max: If API costs exceed $100/month consistently, Claude Code Max is more cost-effective. Most medium-to-heavy users should default to Max.

Hidden Costs

  • Context accumulation: Opus sessions tend to be longer (more complex tasks), accumulating more context. A 30-turn Opus session can reach $20+.
  • Retry loop magnification: Retry loops on Opus cost 5x more per cycle than Sonnet. A single 5-retry loop on Opus: $12.50 vs $2.50 on Sonnet.
  • Subagent overhead: Subagents on Opus cost $0.075+ per spawn (5K tokens x $15/MTok) vs $0.015 on Sonnet. Ten subagents: $0.75 vs $0.15.

Recommendation

Default to Sonnet 4.6 for everything. Create an alias for Opus:

# ~/.zshrc
export CLAUDE_MODEL="claude-sonnet-4-6"
alias claude-opus='claude --model claude-opus-4-6'
# Use Sonnet by default
claude "Fix the null check in auth.ts"
# Explicitly choose Opus for architecture
claude-opus "Design the event sourcing module for the billing system"

This approach delivers 80% of Opus quality at 20% of the cost. The 20% of tasks where Opus genuinely outperforms (architecture, complex debugging) are identifiable before starting.

A useful heuristic: if the task description fits in one sentence, use Sonnet. If it requires a paragraph to describe, consider Opus. If it requires multiple paragraphs, decompose the task before choosing a model.

Cost Calculator

Monthly cost = (Sonnet tasks x $0.45 avg) + (Opus tasks x $3.50 avg)
Example: 20 tasks/day, 80% Sonnet / 20% Opus, 22 working days
= (20 x 0.8 x $0.45 x 22) + (20 x 0.2 x $3.50 x 22)
= $158.40 + $308.00
= $466.40/month
Compared to all-Opus: 20 x $3.50 x 22 = $1,540/month
Savings: $1,073.60/month (69.7%)

Model Routing Rules for CLAUDE.md

Codify model routing decisions in CLAUDE.md so the entire team follows the same logic:

# CLAUDE.md
## Model Selection Guide
### Use Sonnet 4.6 (default) for:
- Bug fixes in 1-3 files
- Feature additions with clear specifications
- Test writing and updating
- Refactoring within a single module
- Documentation updates
- Configuration changes
- Code review and PR feedback
### Use Opus 4.6 (explicit override) for:
- Designing new modules or systems
- Debugging issues that span 5+ files with unclear root cause
- Performance optimization requiring algorithmic analysis
- Security-sensitive code review
- Large-scale pattern changes across many files
### Use Haiku 4.5 for:
- Variable renaming
- Import organization
- Simple formatting fixes
- Adding console.log statements for debugging
- Trivial one-line changes

Transitioning from All-Opus to Mixed Model

For teams currently using Opus for everything, transition gradually:

Week 1: Switch default to Sonnet. Use Opus explicitly for 100% of tasks (override every time). This establishes the habit of conscious model choice.

Week 2: Use Sonnet without override for simple tasks (bug fixes, tests). Continue Opus for everything else. Track task success rates.

Week 3: Expand Sonnet usage to features and refactoring. Opus only for architecture and complex debugging.

Week 4: Full mixed-model workflow. Review cost data to confirm savings.

Expected cost trajectory:

  • Week 0 (all Opus): $500/month
  • Week 1 (conscious choice): $450/month
  • Week 2 (simple on Sonnet): $300/month
  • Week 3 (mostly Sonnet): $175/month
  • Week 4 (optimized mix): $150/month

The transition consistently shows that developers overestimate the quality gap between Sonnet and Opus for routine tasks. After two weeks of side-by-side comparison, most developers report no noticeable difference on standard feature work and bug fixes. The quality gap only becomes apparent on tasks requiring deep architectural reasoning, novel algorithm design, or debugging complex race conditions – tasks that represent fewer than 20% of most development workflows.

Which model? → Take the 5-question quiz in our Model Selector.

Try it: Estimate your monthly spend with our Cost Calculator.

See Also