Claude 3.5 Sonnet vs Claude 3 Opus: Which Should You Use?

Claude 3.5 Sonnet launched last week with benchmark scores exceeding Claude 3 Opus, which was Anthropic's flagship model just a week ago. That raises an obvious question: should you switch? We tested both models extensively over the past week. Here's what we found. ## Performance Comparison Claude 3.5 Sonnet wins on most standardized benchmarks: | Benchmark | Claude 3 Opus | Claude 3.5 Sonnet | What It Measures | |-----------|---------------|-------------------|------------------| | GPQA | 50.4% | 59.4% | Graduate-level reasoning | | HumanEval | 84.9% | 92.0% | Code generation | | MMLU | 86.8% | 88.7% | General knowledge | | MATH | 60.1% | 71.1% | Mathematical reasoning | | Visual QA | Strong | Stronger | Image understanding | On paper, 3.5 Sonnet is better across the board. ## Speed and Cost The speed difference is immediately noticeable: **Claude 3 Opus:** - Average response time: 15-20 seconds for complex prompts - Pricing: $15 per million input tokens, $75 per million output tokens **Claude 3.5 Sonnet:** - Average response time: 7-10 seconds for similar prompts - Pricing: $3 per million input tokens, $15 per million output tokens - **5x cheaper for output tokens** For API users processing significant volume, the cost difference is substantial. A workload generating 10 million output tokens monthly costs $750 with Opus versus $150 with 3.5 Sonnet. ## Real-World Testing Results We tested both models on typical business operations tasks: **Document Analysis** Task: Analyze a 40-page vendor contract and summarize key terms. - Opus: Thorough analysis, found all major clauses, took 18 seconds - 3.5 Sonnet: Equally thorough, found same clauses, took 9 seconds **Result:** Tied on accuracy, 3.5 Sonnet wins on speed. **Code Debugging** Task: Debug a Python script with a subtle logic error. - Opus: Identified the issue, suggested fix with explanation - 3.5 Sonnet: Identified the issue faster, provided more detailed explanation of why it was wrong **Result:** 3.5 Sonnet wins. **Complex Reasoning** Task: Evaluate three different approaches to a business process problem, considering tradeoffs. - Opus: Solid analysis, considered most factors, structured comparison - 3.5 Sonnet: Equally solid analysis, slightly better structure, identified one edge case Opus missed **Result:** 3.5 Sonnet wins marginally. **Creative Writing** Task: Draft executive summary for a quarterly board report. - Opus: Professional tone, good structure, appropriate level of detail - 3.5 Sonnet: Very similar output, hard to distinguish in quality **Result:** Tied. **Visual Analysis** Task: Extract key metrics from a dashboard screenshot with multiple charts. - Opus: Accurate extraction, some formatting inconsistencies - 3.5 Sonnet: More accurate, better formatting, identified chart relationships **Result:** 3.5 Sonnet wins. ## When Claude 3 Opus Still Makes Sense Despite 3.5 Sonnet's benchmark advantages, there are scenarios where Opus might still be preferable: **Extreme edge cases:** Opus has been in production longer and may handle certain unusual inputs more reliably. **Risk-averse production systems:** If you've already validated Opus for a critical application, switching introduces re-validation work. **Specific domain performance:** Your particular use case might perform differently than general benchmarks. But honestly, these scenarios are becoming edge cases. For most applications, 3.5 Sonnet is the better choice. ## Migration Considerations **For API users:** Switching is straightforward - update your model parameter from `claude-3-opus-20240229` to `claude-3-5-sonnet-20240620`. Test on a sample of your typical inputs before switching production traffic. **For web users:** Just select Claude 3.5 Sonnet from the model dropdown at claude.ai. Your conversation history remains accessible. **Testing approach:** Run parallel testing for a week. Send the same prompts to both models and compare outputs. Most users find 3.5 Sonnet meets or exceeds Opus quality while being noticeably faster. ## Cost Impact Example Typical API usage for a medium-sized operations team: - 50 million input tokens/month (analyzing documents, generating reports) - 10 million output tokens/month (generated content) **Claude 3 Opus:** - Input: 50M × $15/M = $750 - Output: 10M × $75/M = $750 - **Total: $1,500/month** **Claude 3.5 Sonnet:** - Input: 50M × $3/M = $150 - Output: 10M × $15/M = $150 - **Total: $300/month** **Savings: $1,200/month** while getting better performance. ## Quick Takeaway Claude 3.5 Sonnet outperforms Claude 3 Opus on most tasks, responds twice as fast, and costs 5x less. Unless you have a specific validated use case where Opus performs better, switch to 3.5 Sonnet. For new projects, start with 3.5 Sonnet. For existing Opus deployments, test 3.5 Sonnet and migrate if results are comparable or better - which they likely will be.