Claude Code Sonnet vs Haiku (2026)

Quick Verdict

Haiku 4.5 ($0.80/$4 per MTok) handles 30-40% of typical Claude Code tasks with equivalent quality to Sonnet 4.6 ($3/$15 per MTok) at 73% lower input cost and 73% lower output cost. Simple code generation, formatting, test writing, and documentation tasks do not require Sonnet’s advanced reasoning. Routing these tasks to Haiku saves $15-$40 per month for a developer currently spending $60-$100 on all-Sonnet usage.

Pricing Breakdown

Model Input Cost Output Cost Blended Rate (est.) Relative Cost
Haiku 4.5 $0.80/MTok $4.00/MTok ~$1.60/MTok 1x (baseline)
Sonnet 4.6 $3.00/MTok $15.00/MTok ~$6.00/MTok 3.75x
Opus 4.6 $15.00/MTok $75.00/MTok ~$30.00/MTok 18.75x

Blended rate assumes 60% input / 40% output token mix.

Feature-by-Feature Cost Analysis

Simple Code Generation

Tasks where Haiku matches Sonnet quality:

# Haiku-appropriate: generate a utility function
claude --model haiku -p "Write a TypeScript function that validates
an email address using a regex. Include JSDoc comments."
# Cost: ~5K tokens x $1.60/MTok = $0.008
# Same task on Sonnet:
# Cost: ~5K tokens x $6.00/MTok = $0.030

Savings: 73% ($0.022 per task)

Complex Debugging and Architecture

Tasks where Sonnet outperforms Haiku:

# Sonnet-appropriate: multi-file debugging
claude -p "The payment webhook is silently failing for subscriptions
with annual billing. Trace the flow from stripe-webhook.ts through
the subscription service to find why annual plans are skipped."
# Sonnet cost: ~80K tokens x $6.00/MTok = $0.48
# Haiku would likely need 2-3x more turns (retries, wrong paths): ~200K tokens x $1.60/MTok = $0.32
# BUT Haiku's solution quality is lower -- may miss the root cause entirely

For complex debugging, Sonnet’s higher per-token cost is offset by fewer tokens needed (correct diagnosis faster) and higher solution quality.

Test Writing

A strong Haiku use case – test patterns are well-defined:

# Haiku: generate tests for a service
claude --model haiku -p "Write Jest tests for src/services/user.ts.
Test: createUser (success + duplicate email error),
getUser (found + not found), deleteUser (success + not found).
Use mocked Prisma client."
# Cost: ~15K tokens x $1.60/MTok = $0.024
# Sonnet equivalent: $0.090

Savings: 73% ($0.066 per test generation task)

Documentation Generation

# Haiku: generate JSDoc comments
claude --model haiku -p "Add JSDoc comments to all exported functions
in src/utils/string.ts. Include @param and @returns tags."
# Cost: ~8K tokens x $1.60/MTok = $0.013
# Sonnet equivalent: $0.048

Code Review

Mixed – depends on review depth:

# Surface-level review (Haiku adequate):
claude --model haiku --allowedTools "Read,Glob,Grep" \
  -p "Check src/api/routes/users.ts for obvious bugs, missing error handling,
  and style issues."
# Cost: ~20K tokens x $1.60/MTok = $0.032
# Deep security review (Sonnet required):
claude --allowedTools "Read,Glob,Grep" \
  -p "Perform a security audit of the authentication flow across
  src/middleware/auth.ts, src/services/auth.ts, and src/routes/auth.ts.
  Check for OWASP Top 10 vulnerabilities."
# Cost: ~60K tokens x $6.00/MTok = $0.36

Real-World Monthly Estimates

All-Sonnet Usage (Current Baseline)

Task Category Tasks/Month Avg Tokens Monthly Cost
Complex debugging 20 80K $9.60
Feature implementation 40 60K $14.40
Test writing 30 15K $2.70
Code review 25 30K $4.50
Documentation 15 8K $0.72
Simple generation 30 5K $0.90
Total 160   $32.82

Optimized Model Routing

Task Category Model Tasks/Month Avg Tokens Monthly Cost
Complex debugging Sonnet 20 80K $9.60
Feature implementation Sonnet 40 60K $14.40
Test writing Haiku 30 15K $0.72
Code review (surface) Haiku 15 20K $0.48
Code review (deep) Sonnet 10 60K $3.60
Documentation Haiku 15 8K $0.19
Simple generation Haiku 30 5K $0.24
Total   160   $29.23

Monthly savings: $3.59 (11%) from Claude Code router guide alone. Combined with other optimizations (context engineering, –max-turns), total savings reach $15-$40/month.

Hidden Costs

Haiku Retries

Haiku occasionally fails on tasks that require multi-step reasoning, leading to retries:

  • Retry rate on complex tasks: 30-50% higher than Sonnet
  • Cost per retry: 50-100% of original task cost
  • Net savings eroded: A task that costs $0.008 on Haiku but retries twice costs $0.024 – nearly matching Sonnet’s $0.030

This is why routing matters: send Haiku only tasks where it succeeds reliably on the first attempt.

Context Window Differences

Both Haiku 4.5 and Sonnet 4.6 support 200K context windows. No difference in session length capability, but Haiku uses tokens less efficiently on complex reasoning, potentially requiring more turns.

Recommendation

Task Type Recommended Model Confidence
Simple code generation Haiku 4.5 High
Test writing (standard patterns) Haiku 4.5 High
Documentation / JSDoc Haiku 4.5 High
Formatting / linting fixes Haiku 4.5 High
Bug fixing (single file) Sonnet 4.6 Medium
Multi-file refactoring Sonnet 4.6 High
Complex debugging Sonnet 4.6 High
Architecture decisions Sonnet 4.6 / Opus 4.6 High
Security review Sonnet 4.6 High

Implementing Model Routing in Practice

Set up shell aliases and CLAUDE.md rules to enforce model routing:

# ~/.zshrc -- model routing aliases
alias cq='claude --model haiku --max-turns 8'     # Quick/simple tasks
alias cs='claude --model sonnet --max-turns 20'    # Standard tasks
alias co='claude --model opus --max-turns 25'      # Complex reasoning
# Decision helper script
claude-route() {
  echo "Task complexity?"
  echo "  1. Simple (docs, formatting, simple generation) -> Haiku"
  echo "  2. Standard (bug fix, feature, review) -> Sonnet"
  echo "  3. Complex (architecture, multi-system debug) -> Opus"
  read -r choice
  case $choice in
    1) claude --model haiku --max-turns 8 -p "$*" ;;
    2) claude --model sonnet --max-turns 20 -p "$*" ;;
    3) claude --model opus --max-turns 25 -p "$*" ;;
    *) echo "Invalid choice" ;;
  esac
}

Add routing guidance to CLAUDE.md for automated workflows:

# CLAUDE.md -- Model Routing
## Model Selection (for CI/automation)
- Documentation tasks: use --model haiku
- PR review (surface): use --model haiku
- PR review (security): use --model sonnet
- Bug fix: use --model sonnet
- Architecture design: use --model opus (rarely needed)

Monitoring Model Routing Effectiveness

Track the cost per task type to validate routing decisions:

# After implementing model routing, compare weekly costs
ccusage --sort date --limit 40
# Look for:
# - Haiku sessions: should be <$0.05 each
# - Sonnet sessions: should be <$0.50 each
# - If Haiku sessions show high retry rates, some tasks need upgrading to Sonnet

Review routing decisions monthly. If Haiku fails more than 20% of the time on a task category, promote that category to Sonnet. The retry cost on Haiku (double the tokens for a failed + retried attempt) can exceed the cost difference versus just using Sonnet upfront.

Cost Calculator

Current monthly Sonnet spend: $___
Haiku-eligible percentage (estimate 30-40%): ___%
Estimated savings = current_spend x haiku_percentage x 0.73
Example:
  $60/month x 35% Haiku-eligible x 0.73 savings = $15.33/month saved
  New monthly cost: $60 - $15.33 = $44.67

Haiku 4.5 Limitations to Watch For

Not all “simple” tasks are actually simple from a model perspective. These tasks look simple but require Sonnet-level reasoning:

  • Code with subtle bugs: Haiku may fix the obvious issue but miss a related subtle bug in the same function
  • Cross-file implications: Even simple-looking changes can have cross-file type implications that Haiku misses
  • Unfamiliar libraries: If the codebase uses niche libraries, Haiku’s training may not cover them as well as Sonnet’s
  • Test edge cases: Haiku writes good happy-path tests but may miss important error-path test cases

When in doubt about task complexity, start with Sonnet. The cost of a failed Haiku attempt (~$0.03 for the failed session + ~$0.03 for the Sonnet retry) exceeds the cost of just using Sonnet from the start (~$0.04). Route to Haiku only when confident the task is straightforward.

Haiku for CI Pipelines

CI/CD is the strongest use case for Haiku because CI tasks are predictable and repetitive:

# .github/scripts/haiku-pr-lint.sh
# Use Haiku for fast, cheap PR linting
claude --model haiku --max-turns 5 \
  --allowedTools "Read,Glob,Grep" \
  -p "Check these files for obvious issues: $(git diff --name-only HEAD~1)"
# Cost per PR: ~$0.01-$0.02 (vs $0.05-$0.10 on Sonnet)
# At 50 PRs/week: $2-$4/month on Haiku vs $10-$20 on Sonnet

Automated CI tasks benefit from Haiku because they run frequently, have well-defined scope, and tolerance for occasional misses (human reviewers catch what Haiku misses).

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

Estimate tokens → Calculate your usage with our Token Estimator.

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