A/B Testing and Feature Flags with sub-millisecond performance

Low-latency configuration data at the edge

Configuration data drives everything from A/B tests and feature flags to URL rewrites and request-blocking rules. But conventional configuration management approaches often introduce latency and scaling problems that undercut the very experiments they're meant to enable.

Vercel has now made its Edge Config store generally available—a globally distributed data store built for fast, inexpensive reads and infrequent writes. Because data is actively replicated to all Vercel regions before it is requested, lookups happen without a round-trip to a central origin.

import { NextResponse, NextRequest } from "next/server";
import { get } from "@vercel/edge-config";
export async function middleware(request: NextRequest) {
  if (await get("showNewDashboard")) {
    return NextResponse.rewrite(new URL("/new-dashboard", request.url));
  }
}

Most Edge Config lookups return in 0ms, and 99% complete in under 10ms, getting close to the performance of static configuration while still allowing updates from the API or UI. Changes propagate to every region within seconds, so teams can modify experiments or rules without triggering a full site redeployment.

Edge Config integrates directly with experimentation platforms. With Statsig, evaluation rules can be populated automatically into the Edge Config connected to your project; changes made in Statsig's interface are then queryable from routing middleware at near-zero latency. Split is upgrading its integration to support Edge Config, and a LaunchDarkly integration became available at the end of April.

"LaunchDarkly and Vercel's mutual enterprise customers now have a way to deploy feature flags and experiments at the edge with zero latency."

— John Kodumal, Co-Founder and CTO, LaunchDarkly

"Combining Statsig with Next.js and Vercel Edge Config unlocks a high-performance feature management and experimentation engine in a way that was just not possible before."

— Vijaye Raji, Founder and CEO, Statsig

"The globally consistent and dynamic nature of the data storage offered by Edge Config makes it the perfect fit for Split feature flags SDK to work at the edge."

— Pato Echague, Co-Founder and CTO, Split

Dynamic routing and security rules

Pairing Edge Config with Vercel's Routing Middleware enables dynamic control over routing decisions. For instance, blocked IPs and user agents can be stored in Edge Config, then fetched once in middleware as a complete list to reject unwanted requests with minimal overhead. The same mechanism supports more advanced policies such as geolocation-based blocking.

import { getAll } from "@vercel/edge-config";
export async function middleware(request: Request) {
  const [userAgents, ipAddresses] = await getAll(["userAgents", "ipAddresses"]);
  if (
    userAgents.includes(request.headers.get("user-agent")) ||
    ipAddresses.includes(request.ip)
  ) {
    return new Response("Denied", { status: 403 });
  }
}

Availability and pricing

Edge Config is available on every Vercel account. Hobby users get 50,000 reads per month; Pro and Enterprise plans include 1,000,000 reads per month, with additional reads available for purchase. Read and write counts are visible in the account dashboard.

To start, deploy one of the example templates or consult the documentation for setup details.