Should I switch my API routes to the edge runtime to avoid cold starts?

I wouldn't. Edge functions run close to the user, your database is in one place. So a user in Sydney hits an edge function in Sydney, which then makes every query to your Supabase in Europe. That's likely why it sometimes feels slower.

Also, cold starts on Vercel's Node runtime are much less of a thing than they used to be (fluid compute reuses instances). Before changing runtimes, find out what the slow requests actually are: check the function duration in the logs. Random 1-2s is often a slow OpenAI call or a region mismatch, not a cold start.

Slight disagreement: edge is fine for routes that don't touch your database. Redirects, geolocation, A/B cookie logic, OG images, or a thin proxy that streams from OpenAI are all good edge candidates. The rule I use: if it talks to your database more than once, run it next to the database.

Measure before and after with a fixed test: 20 requests to the route with curl -w "%{time_total}\n". One click in the browser is too noisy to tell edge from node.