I followed the instructions and have my routes/+layout.ts file as below:
import { dev } from "$app/environment";
import { injectAnalytics } from "@vercel/analytics/sveltekit";
import { injectSpeedInsights } from "@vercel/speed-insights/sveltekit";
injectAnalytics({ mode: dev ? "development" : "production" });
injectSpeedInsights();
The description said that I should expect the script to be inside the body tag, but when I checked, it's still in the head tag along with analytics script.