Model Migration & Comparison
When migrating between models or selecting the best model for your use case, evaluation provides objective evidence to guide your decision. This guide demonstrates how to compare models systematically.Why Compare Models
Model comparison helps you:- Make informed decisions: Use data instead of intuition
- Validate upgrades: Ensure new models perform better
- Optimize costs: Balance performance with pricing
- Meet requirements: Verify models meet your quality standards
- Support migration: Smooth transition from legacy models
Migration Scenarios
Common Migration Paths
PaLM to Gemini
Upgrade from legacy PaLM models to modern Gemini models
Model Versions
Compare different versions of the same model (e.g., Gemini 1.5 to 2.0)
Size Variants
Balance performance vs. cost (Flash vs. Pro)
Custom Models
Evaluate fine-tuned models against base models
Evaluation Setup
Installation
Initialize Vertex AI
Preparing Evaluation Data
Create Representative Dataset
Use real examples from your use case:Use at least 100 examples for statistically significant results. These 5 examples are for demonstration.
Select Evaluation Metrics
Choose metrics aligned with your quality requirements:Comparing Two Models
Example: PaLM to Gemini Migration
Visualization
Radar Plot Comparison
Compare qualitative metrics:Bar Plot Comparison
Compare quantitative metrics:Comparing Multiple Models
Evaluate several candidates simultaneously:Comparing Model Configurations
Test different settings for the same model:Interpretation Guidelines
Understanding Metric Scores
- Model-Based Metrics
- ROUGE
- BLEU
Scale: 1-5
- 5: Excellent - Exceeds expectations
- 4: Good - Meets most requirements
- 3: Fair - Acceptable with room for improvement
- 2: Poor - Below standards
- 1: Very Poor - Unacceptable
- Mean scores across dataset
- Standard deviation (consistency)
- Per-example explanations
Making Migration Decisions
Compare summary metrics
Look at mean scores across all evaluation examples. The model with consistently higher scores across important metrics is generally preferable.
Assess consistency
Check standard deviations. Lower variance indicates more predictable performance.
Consider costs
Balance performance improvements against pricing differences:
- Flash models: Faster, cheaper, good for most tasks
- Pro models: Higher quality, more expensive, better for complex tasks
Example Decision Matrix
| Model | Coherence | Fluency | ROUGE | Cost | Latency | Recommendation |
|---|---|---|---|---|---|---|
| text-bison | 3.2 | 3.6 | 0.23 | $ | 800ms | Baseline |
| gemini-2.0-flash | 4.0 | 4.6 | 0.33 | $ | 400ms | ✅ Recommended |
| gemini-1.5-pro | 4.4 | 4.8 | 0.36 | $$$ | 1200ms | High-quality use cases |
Advanced Comparison
Prompt Variations
Test how models respond to different prompt styles:Domain-Specific Comparison
Evaluate models on your specific domain:Tracking Over Time
Experiments for Version Control
Organize evaluations by experiment:Best Practices
Use Production Data
Evaluate on real examples from your application for accurate assessment
Multiple Metrics
No single metric tells the full story - use a balanced set
Sufficient Examples
100+ examples provide statistical significance
Version Control
Track evaluations over time to measure improvements
Cost Consideration
Factor in pricing when comparing similar performance
Stakeholder Input
Involve domain experts in interpreting results
Common Pitfalls
Small Dataset
❌ Problem: Testing with only 5-10 examples ✅ Solution: Use at least 100 representative examplesSingle Metric Focus
❌ Problem: Deciding based only on ROUGE or coherence ✅ Solution: Evaluate multiple complementary metricsIgnoring Edge Cases
❌ Problem: Only looking at average scores ✅ Solution: Review worst-performing examplesNo Baseline
❌ Problem: Evaluating new model without comparing to current ✅ Solution: Always evaluate baseline for contextExample: Complete Migration Workflow
Next Steps
View Results
Access evaluation reports in Vertex AI console
Evaluation Overview
Learn more about evaluation concepts
Model Garden
Explore available models
Pricing
Compare model costs