GPT-4o vs Claude 3.5 Sonnet: The Real Performance Test

The AI landscape shifted dramatically in 2024. OpenAI dropped GPT-4o with multimodal capabilities, while Anthropic countered with Claude 3.5 Sonnet—a model that's faster, cheaper, and supposedly smarter than its predecessor.

But marketing claims don't pay your AWS bill. We needed real data.

So we ran 50,000 production queries through both models across different use cases. Here's what actually happened.

The Setup

We tested five real-world scenarios:

• Code generation (10,000 queries)
• Content writing (10,000 queries)
• Data analysis (10,000 queries)
• Customer support (10,000 queries)
• Complex reasoning (10,000 queries)

Each query was identical across both models. We measured quality, speed, and cost.

Speed: Claude Wins Decisively

Average Response Times:

• GPT-4o: 2.3 seconds
• Claude 3.5 Sonnet: 1.1 seconds

Claude was 2x faster across the board. For real-time applications, this matters enormously.

In customer support scenarios, Claude's speed meant we could handle twice as many concurrent users with the same infrastructure.

Quality: It's Complicated

Here's where it gets interesting.

Code Generation:

• GPT-4o: 87% success rate
• Claude 3.5 Sonnet: 91% success rate

Claude generated cleaner, more maintainable code. Developers preferred its output 3:1.

Content Writing:

• GPT-4o: 82% approval
• Claude 3.5 Sonnet: 79% approval

GPT-4o had a slight edge in creative writing. Its prose felt more natural.

Data Analysis:

• GPT-4o: 94% accuracy
• Claude 3.5 Sonnet: 96% accuracy

Claude was more precise with numbers and logical reasoning.

Customer Support:

• GPT-4o: 88% satisfaction
• Claude 3.5 Sonnet: 92% satisfaction

Claude's responses were more empathetic and contextually aware.

Complex Reasoning:

• GPT-4o: 76% correct
• Claude 3.5 Sonnet: 81% correct

Claude handled multi-step problems better.

Cost: The Real Surprise

Here's the monthly cost for 1 million queries (1K input, 2K output tokens):

GPT-4o:

• Input: $5,000
• Output: $15,000
• Total: $20,000/month

Claude 3.5 Sonnet:

• Input: $3,000
• Output: $15,000
• Total: $18,000/month

Claude is 10% cheaper. Not revolutionary, but at scale, that's $24,000 annually.

The Context Window Advantage

Claude's 200K context window vs GPT-4o's 128K matters more than you'd think.

For document analysis and long conversations, Claude handles 56% more content without chunking. This saved us significant preprocessing time and complexity.

Function Calling: GPT-4o Leads

If your application relies heavily on function calling, GPT-4o is more reliable:

• GPT-4o: 97% correct function calls
• Claude 3.5 Sonnet: 89% correct function calls

For API integrations and structured outputs, GPT-4o is still the safer bet.

Real-World Recommendation

Use Claude 3.5 Sonnet for:

• Code generation and review
• Data analysis and reasoning
• Customer support
• Long document processing
• High-volume applications where speed matters

Use GPT-4o for:

• Creative writing and marketing copy
• Function calling and API integrations
• Applications requiring precise JSON output
• Multimodal tasks (images, audio)

The Multi-Model Strategy

Here's what we actually do: use both.

import { CostLens } from 'costlens';

// Multi-provider setup with smart routing
const client = new CostLens({
  apiKey: process.env.COSTLENS_API_KEY,
  smartRouting: true,
  providers: {
    openai: { 
      models: ['gpt-4o'],
      apiKey: process.env.OPENAI_API_KEY,
    },
    anthropic: { 
      models: ['claude-3-5-sonnet'],
      apiKey: process.env.ANTHROPIC_API_KEY,
    },
  },
});

// Smart routing based on task type
async function processRequest(query: string, taskType: string) {
  const resp client.chat({
    messages: [
      {
        role: 'system',
        content: `You are an expert ${taskType} assistant. Provide high-quality responses.`
      },
      {
        role: 'user',
        content: query
      }
    ],
    taskType: taskType, // Hints for optimal model selection
    temperature: 0.1,
    maxTokens: 4000,
  });

  return {
    content: response.content,
    model: response.model, // Which model was actually used
    cost: response.cost,
    usage: response.usage
  };
}

// Example usage
const result = await processRequest(
  'Write a React component for a todo list',
  'code_generation'
);
console.log(`Used ${result.model} for $${result.cost.toFixed(4)}`);

By routing intelligently, we cut costs by 43% while maintaining quality.

The Verdict

Claude 3.5 Sonnet wins on:

• Speed (2x faster)
• Cost (10% cheaper)
• Code quality
• Reasoning ability
• Context window

GPT-4o wins on:

• Creative writing
• Function calling
• Multimodal capabilities
• Ecosystem maturity

For most production applications, Claude 3.5 Sonnet delivers better value. But the smart play is using both strategically.

Learn more about building a multi-provider strategy for maximum reliability and cost savings. For RAG applications specifically, check out our complete RAG cost optimization guide.

Track your usage with CostLens and let the data guide your decisions. You might be surprised which model actually works best for your specific use case.