Next.js 16 vs Fastify + React
Real-world performance comparison based on identical SaaS dashboard implementations.
Next.js 16
Vercel
Next.js deployed on its native platform—the way it was designed to run. Vercel's infrastructure is purpose-built for Next.js, providing automatic edge caching, instant rollbacks, and preview deployments for every git push. ISR (Incremental Static Regeneration) works seamlessly on Vercel with on-demand revalidation APIs and automatic cache invalidation across their global edge network. Edge Functions run your middleware in 30+ regions with sub-millisecond cold starts. This deployment demonstrates Next.js at its most optimized, with Vercel handling image optimization, analytics, and Web Vitals monitoring automatically.
Performance Metrics
Lower is better for all metrics. Green indicates the faster framework.
| Metric | Next.js 16 | Fastify + React | Winner |
|---|---|---|---|
| TTFB (p50) | 44.7ms | 340.9ms | ◀ |
| TTFB (p95) | 44.86ms | 402.72ms | ◀ |
| LCP (p50) | 62ms | 370ms | ◀ |
| LCP (p95) | 70.2ms | 430.6ms | ◀ |
| CLS | 0 | 0 | = |
| TBT | 0 ms | 0 ms | = |
| LCP → TTFB | N/A | N/A | - |
| LCP → Load Delay | N/A | N/A | - |
| LCP → Load Duration | N/A | N/A | - |
| LCP → Render Delay | N/A | N/A | - |
| Performance Score | 96 | 96 | = |
| SEO Score | 100 | 92 | ◀ |
| Accessibility Score | 88 | 80 | ◀ |
| Best Practices Score | 100 | 100 | = |
LLM Understanding (Claude Opus 4.5)
How efficiently Claude Opus 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | Next.js 16 | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3883ms | N/A | - |
| Exploration Tokens | 3963 | N/A | - |
| Files Examined | 11 | N/A | - |
| Validation Accuracy | 100% | N/A | - |
| Time Per File | 353ms | N/A | - |
| Tokens Per File | 3245 | N/A | - |
| Efficiency Score | 43.28 | N/A | - |
LLM Understanding (Claude Haiku 4.5)
How efficiently Claude Haiku 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | Next.js 16 | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3029ms | N/A | - |
| Exploration Tokens | 3991 | N/A | - |
| Files Examined | 11 | N/A | - |
| Validation Accuracy | 99% | N/A | - |
| Time Per File | 275ms | N/A | - |
| Tokens Per File | 3225 | N/A | - |
| Efficiency Score | 55.84 | N/A | - |
Build Metrics
| Metric | Next.js 16 | Fastify + React | Winner |
|---|---|---|---|
| Bundle Size (JS) | 613.3KB | 285.3KB | ▶ |
| Bundle Size (CSS) | 23.3KB | 23.1KB | ▶ |
| Build Time | 0s | 2.5s | ◀ |
| Dependencies | 18 | 21 | ◀ |
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