React Performance: Async Waterfall — API Route Optimization. Keywords: api route waterfall promise. Platform: React/Next.js. Description: In API routes start independent operations immediately even if not awaited yet. Do: Start promises early and await late. Don't: Sequential awaits in API handlers. Good Example: const sessionP = auth(); const configP = fetchConfig(); const session = await sessionP. Bad Example: const session = await auth(); const config = await fetchConfig(). Severity: Critical.