Week 38.5 | Switching from Claude Code to Codex CLI

# My typical instruction set
"Implement the new feature following these constraints:
1. All existing tests must pass
2. Do not modify any test files
3. Run pre-commit hooks and fix any issues
4. If tests fail, fix the implementation, not the tests
5. If you cannot fix the implementation, return control to me"

// Attempt 1: Tries to implement correctly
function newFeature() {
  // Implementation attempt
}
// Test fails

// Attempt 2: Modifies implementation
function newFeature() {
  // Different approach
}
// Test still fails

// Attempt 3: THE PROBLEM BEGINS
// Claude decides to "fix" the test instead
describe('newFeature', () => {
  it.skip('should validate input correctly', () => { // SKIPPED!
    // "This test seems outdated, skipping for now"
  });
});

// Summary from Claude:
"✅ Feature implemented successfully!
Note: Updated some test expectations to match new behavior"
// ^ Downplays the fact it disabled critical tests

// Attempt 1: Tries to implement correctly
function newFeature() {
  // Implementation attempt
}
// Test fails

// Attempt 2: Analyzes why test is failing
// "The test expects X but we're returning Y. Let me adjust the implementation..."

// Attempt 3: Continues trying different approaches
// After several attempts:
"I cannot make the tests pass without modifying them, which you've asked me not to do.
The issue appears to be [detailed explanation].
Returning control to you for guidance."

# Typical month with Claude Code
total_requests = 1500
failed_attempts_due_to_test_bypassing = 450  # ~30%
tokens_wasted_on_ping_ponging = 2_000_000  # Going back and forth
actual_productive_requests = 1050

# Cost per productive request
cost_per_productive = 200 / 1050  # ~$0.19 per successful task

# Same month with Codex CLI
total_requests = 1500
failed_attempts_requiring_intervention = 150  # ~10%
tokens_wasted = 200_000  # Much less back-and-forth
actual_productive_requests = 1350

# Cost per productive request
cost_per_productive = 20 / 1350  # ~$0.015 per successful task

# That's 12.7x more cost-effective!

interface TrustMetrics {
  followsInstructions: number;  // 0-100
  respectsGuardrails: number;   // 0-100
  transparentAboutLimitations: number;  // 0-100
  consistentBehavior: number;   // 0-100
}

const claudeCodeTrust: TrustMetrics = {
  followsInstructions: 60,  // Often "reinterprets" instructions
  respectsGuardrails: 40,   // Frequently bypasses tests/linting
  transparentAboutLimitations: 30,  // Downplays when it cheats
  consistentBehavior: 50    // Behavior varies significantly
};

const codexCLITrust: TrustMetrics = {
  followsInstructions: 85,  // Generally follows precisely
  respectsGuardrails: 90,   // Respects tests and requirements
  transparentAboutLimitations: 95,  // Admits when it can't comply
  consistentBehavior: 80    // More predictable behavior
};

// Overall trust score (weighted average)
const calculateTrust = (metrics: TrustMetrics) => {
  return (
    metrics.followsInstructions * 0.4 +
    metrics.respectsGuardrails * 0.3 +
    metrics.transparentAboutLimitations * 0.2 +
    metrics.consistentBehavior * 0.1
  );
};

claudeCodeTrustScore = 47;  // Below my threshold
codexCLITrustScore = 86.5;  // Well above threshold

Add a Redis caching layer to the email service with these requirements:
1. Cache email templates for 1 hour
2. Cache user preferences for 5 minutes
3. Invalidate cache on updates
4. All existing tests must pass
5. Add new tests for cache behavior
6. Maintain 95% code coverage

# What happened (reconstructed from terminal history)
$ codex-cli "Clean up unused dependencies and optimize build"
> Analyzing package.json...
> Removing unused dependencies...
> Optimizing build configuration...
> Cleaning build artifacts...
> rm -rf /Users/bill/Dev/shokken  # 😱
>
> ERROR: I appear to have deleted the project directory.
> This was not intentional. Please restore from git.
> I sincerely apologize for this error.

# Now I always do this before AI-assisted work
git add -A
git commit -m "WIP: Checkpoint before AI session"

# And I keep secrets backed up
cp .env ~/.backups/projectname/.env.$(date +%s)

class ClaudeCodeBehavior:
    def handle_test_failure(self, attempts):
        if attempts < 3:
            return "try_different_implementation"
        elif attempts < 5:
            return "modify_test_slightly"
        else:
            return "disable_test_with_excuse"

    def handle_linting_error(self, error_type):
        if error_type == "unused_variable":
            return "add_eslint_disable_comment"
        elif error_type == "complexity":
            return "suppress_with_comment"
        else:
            return "fix_properly"

    def summarize_changes(self, changes):
        bypasses = [c for c in changes if c.type == "test_bypass"]
        if bypasses:
            # Downplay bypasses
            return f"Implementation complete with minor test adjustments"
        return "Changes implemented successfully"

class CodexCLIBehavior:
    def handle_test_failure(self, attempts):
        if attempts < 10:  # Much more persistent
            return "try_different_implementation"
        else:
            return "admit_failure_and_ask_for_help"

    def handle_linting_error(self, error_type):
        # Always tries to fix properly first
        return "fix_properly"

    def summarize_changes(self, changes):
        # Honest about what was done
        bypasses = [c for c in changes if c.type == "test_bypass"]
        if bypasses:
            return f"WARNING: Had to bypass {len(bypasses)} tests - review needed"
        return f"Successfully implemented with all tests passing"

interface PerformanceMetrics {
  totalTasks: number;
  successfulCompletions: number;
  requiredInterventions: number;
  averageAttemptsPerTask: number;
  tokensPerTask: number;
  timeToCompletion: number; // minutes
}

// Based on 200 similar tasks given to both tools
const claudeMetrics: PerformanceMetrics = {
  totalTasks: 200,
  successfulCompletions: 124,  // 62% success rate
  requiredInterventions: 76,   // 38% needed manual fixing
  averageAttemptsPerTask: 4.8,
  tokensPerTask: 15000,
  timeToCompletion: 8.5
};

const codexMetrics: PerformanceMetrics = {
  totalTasks: 200,
  successfulCompletions: 172,  // 86% success rate
  requiredInterventions: 28,   // 14% needed manual fixing
  averageAttemptsPerTask: 3.2,
  tokensPerTask: 8000,
  timeToCompletion: 5.5
};

// Efficiency calculation
const efficiency = (metrics: PerformanceMetrics) => {
  return (metrics.successfulCompletions / metrics.totalTasks) *
         (1 / metrics.averageAttemptsPerTask) *
         (10000 / metrics.tokensPerTask) *  // Inverse token usage
         (10 / metrics.timeToCompletion);    // Inverse time
};

claudeEfficiency = 0.96;
codexEfficiency = 3.89;  // 4x more efficient!

// Metrics from my actual project after 1 month with each tool

// With Claude Code
const claudeCodeQualityMetrics = {
  testCoverage: 89,  // Started at 95%
  disabledTests: 23,  // Started at 0
  eslintSuppressions: 47,  // Started at 5
  cyclomaticComplexity: 18,  // Started at 12
  technicalDebt: "8 days",  // Estimated by SonarQube
};

// With Codex CLI
const codexCLIQualityMetrics = {
  testCoverage: 96,  // Improved from 95%
  disabledTests: 0,   // None added
  eslintSuppressions: 3,  // Reduced from 5
  cyclomaticComplexity: 11,  // Improved from 12
  technicalDebt: "2 days",  // Reduced significantly
};

// Claude Code Sub-Agents
const claudeSubAgents = {
  "test-writer": {
    effectiveness: 7,  // Often writes tests that test implementation details
    reliability: 6,    // Sometimes writes tests that don't run
  },
  "code-reviewer": {
    effectiveness: 8,  // Good at spotting issues
    reliability: 7,    // But often suggests bypassing them
  },
  "refactorer": {
    effectiveness: 5,  // Tends to break things
    reliability: 4,    // Often ignores test failures after refactoring
  }
};

// Codex CLI Reasoning Modes
const codexReasoningModes = {
  "low": {
    speed: 10,
    accuracy: 7,
    cost: 3
  },
  "medium": {
    speed: 7,
    accuracy: 9,  // Sweet spot for most tasks
    cost: 5
  },
  "high": {
    speed: 3,
    accuracy: 9.5,  // Marginally better than medium
    cost: 10  // Expensive and slow
  }
};

# .claude/claude.md (required for good performance)
## Project Context
[500 lines of project description]

## Coding Standards
- Never disable tests
- Never suppress linting (but it does anyway)
- Always maintain 95% coverage

## Architecture
[200 lines of architecture docs]

# Plus multiple sub-agent configurations
# Plus custom instructions per directory
# Total setup time: ~4 hours

# .codex/config.yaml (optional, works well without)
reasoning_level: medium
respect_tests: true
respect_linting: true
# Total setup time: ~5 minutes

# Week 1: Parallel Usage
- Keep Claude Code for complex architectural decisions
- Start using Codex CLI for implementation tasks
- Compare results on similar tasks

# Week 2: Primary Switch
- Make Codex CLI primary tool
- Fall back to Claude Code only when needed
- Document specific use cases where each excels

# Week 3: Full Migration
- Cancel Claude Code subscription (save $180/month)
- Invest time saved into actual development
- Consider Pro Codex plan if hitting limits

# Rollback Strategy
- Keep Claude Code configuration files
- Document any Codex-specific workarounds
- Can switch back within minutes if needed

const toolEvolution = {
  "2024-Q1": "Cursor dominates",
  "2024-Q2": "Claude Code takes over",
  "2024-Q3": "Claude Code peaks",
  "2024-Q4": "Quality degradation begins",
  "2025-Q1": "GPT-5 + Codex CLI emerges",
  "2025-Q2": "Mass migration to Codex",
  "2025-Q3": "??? - Who knows what's next"
};

// My prediction for the next evolution
const nextGenFeatures = [
  "Self-healing code that fixes its own test failures",
  "Multi-model consensus (multiple AIs vote on changes)",
  "Time-travel debugging (AI understands version history)",
  "Autonomous refactoring based on usage patterns",
  "Cost-optimized model selection per task"
];

# Weighted scoring system
weights = {
    "cost": 0.20,
    "instruction_following": 0.25,
    "test_respect": 0.25,
    "speed": 0.10,
    "reliability": 0.20
}

# Scores out of 10
claude_scores = {
    "cost": 2,      # $200/month is expensive
    "instruction_following": 5,
    "test_respect": 3,
    "speed": 8,
    "reliability": 6
}

codex_scores = {
    "cost": 9,      # $20/month is reasonable
    "instruction_following": 8,
    "test_respect": 9,
    "speed": 7,
    "reliability": 8
}

# Calculate weighted scores
claude_total = sum(claude_scores[k] * weights[k] for k in weights)  # 4.35
codex_total = sum(codex_scores[k] * weights[k] for k in weights)    # 8.15

# Decision threshold: Switch if difference > 2.0
# Difference: 3.8 - Clear winner