diff --git a/.changeset/lazy-dots-sip.md b/.changeset/lazy-dots-sip.md
new file mode 100644
index 00000000000..d812bcc3d57
--- /dev/null
+++ b/.changeset/lazy-dots-sip.md
@@ -0,0 +1,6 @@
+---
+"remix": patch
+"@remix-run/dev": patch
+---
+
+add warning when `future.v2_routeConvention` is not enabled
diff --git a/integration/flat-routes-test.ts b/integration/flat-routes-test.ts
index 9254ca16ee5..49a4937f555 100644
--- a/integration/flat-routes-test.ts
+++ b/integration/flat-routes-test.ts
@@ -5,6 +5,7 @@ import { PlaywrightFixture } from "./helpers/playwright-fixture";
 import type { Fixture, AppFixture } from "./helpers/create-fixture";
 import { createFixtureProject } from "./helpers/create-fixture";
 import { createAppFixture, createFixture, js } from "./helpers/create-fixture";
+import { flatRoutesWarning } from "../packages/remix-dev/config";
 
 let fixture: Fixture;
 let appFixture: AppFixture;
@@ -147,6 +148,51 @@ test.describe("flat routes", () => {
   }
 });
 
+test.describe("warns when v1 routesConvention is used", () => {
+  let buildStdio = new PassThrough();
+  let buildOutput: string;
+
+  let originalConsoleLog = console.log;
+  let originalConsoleWarn = console.warn;
+  let originalConsoleError = console.error;
+
+  test.beforeAll(async () => {
+    console.log = () => {};
+    console.warn = () => {};
+    console.error = () => {};
+    await createFixtureProject({
+      buildStdio,
+      files: {
+        "routes/index.tsx": js`
+          export default function () {
+            return <p>routes/index</p>;
+          }
+        `,
+      },
+    });
+
+    let chunks: Buffer[] = [];
+    buildOutput = await new Promise<string>((resolve, reject) => {
+      buildStdio.on("data", (chunk) => chunks.push(Buffer.from(chunk)));
+      buildStdio.on("error", (err) => reject(err));
+      buildStdio.on("end", () =>
+        resolve(Buffer.concat(chunks).toString("utf8"))
+      );
+    });
+  });
+
+  test.afterAll(() => {
+    console.log = originalConsoleLog;
+    console.warn = originalConsoleWarn;
+    console.error = originalConsoleError;
+  });
+
+  test("warns about conflicting routes", () => {
+    console.log(buildOutput);
+    expect(buildOutput).toContain(flatRoutesWarning);
+  });
+});
+
 test.describe("emits warnings for route conflicts", async () => {
   let buildStdio = new PassThrough();
   let buildOutput: string;
diff --git a/integration/hmr-test.ts b/integration/hmr-test.ts
index 1381038e0e4..63a88293661 100644
--- a/integration/hmr-test.ts
+++ b/integration/hmr-test.ts
@@ -14,6 +14,7 @@ let fixture = (options: { port: number; appServerPort: number }) => ({
       appServerPort: options.appServerPort,
     },
     unstable_tailwind: true,
+    v2_routeConvention: true,
   },
   files: {
     "package.json": `
@@ -124,7 +125,7 @@ let fixture = (options: { port: number; appServerPort: number }) => ({
           );
         }
       `,
-    "app/routes/index.tsx": `
+    "app/routes/_index.tsx": `
         import { useLoaderData } from "@remix-run/react";
         export default function Index() {
           const t = useLoaderData();
@@ -235,7 +236,7 @@ test("HMR", async ({ page }) => {
     await counter.click();
     await page.waitForSelector(`#root-counter:has-text("inc 1")`);
 
-    let indexPath = path.join(projectDir, "app", "routes", "index.tsx");
+    let indexPath = path.join(projectDir, "app", "routes", "_index.tsx");
     let originalIndex = fs.readFileSync(indexPath, "utf8");
     let counterPath = path.join(projectDir, "app", "components", "counter.tsx");
     let originalCounter = fs.readFileSync(counterPath, "utf8");
diff --git a/integration/tsconfig.json b/integration/tsconfig.json
index b8fd6c97ac7..d2215944147 100644
--- a/integration/tsconfig.json
+++ b/integration/tsconfig.json
@@ -17,6 +17,7 @@
     "rootDir": "."
   },
   "references": [
+    { "path": "../packages/remix-dev" },
     { "path": "../packages/remix-express" },
     { "path": "../packages/remix-react" },
     { "path": "../packages/remix-server-runtime" }
diff --git a/packages/remix-dev/__tests__/create-test.ts b/packages/remix-dev/__tests__/create-test.ts
index 4a0fbed9768..4508ac91907 100644
--- a/packages/remix-dev/__tests__/create-test.ts
+++ b/packages/remix-dev/__tests__/create-test.ts
@@ -8,6 +8,7 @@ import stripAnsi from "strip-ansi";
 
 import { run } from "../cli/run";
 import { server } from "./msw";
+import { flatRoutesWarning } from "../config";
 
 beforeAll(() => server.listen({ onUnhandledRequest: "error" }));
 afterAll(() => server.close());
@@ -347,7 +348,9 @@ describe("the create command", () => {
       "--no-typescript",
     ]);
     expect(output.trim()).toBe(
-      getOptOutOfInstallMessage() +
+      flatRoutesWarning +
+        "\n\n" +
+        getOptOutOfInstallMessage() +
         "\n\n" +
         getSuccessMessage(path.join("<TEMP_DIR>", "template-to-js"))
     );
diff --git a/packages/remix-dev/config.ts b/packages/remix-dev/config.ts
index 4c6f161eb86..8686777438a 100644
--- a/packages/remix-dev/config.ts
+++ b/packages/remix-dev/config.ts
@@ -560,9 +560,14 @@ export async function readConfig(
     root: { path: "", id: "root", file: rootRouteFile },
   };
 
-  let routesConvention = appConfig.future?.v2_routeConvention
-    ? flatRoutes
-    : defineConventionalRoutes;
+  let routesConvention: typeof flatRoutes;
+
+  if (appConfig.future?.v2_routeConvention) {
+    routesConvention = flatRoutes;
+  } else {
+    warnOnce(flatRoutesWarning, "v2_routeConvention");
+    routesConvention = defineConventionalRoutes;
+  }
 
   if (fse.existsSync(path.resolve(appDirectory, "routes"))) {
     let conventionalRoutes = routesConvention(
@@ -726,4 +731,6 @@ let listFormat = new Intl.ListFormat("en", {
   type: "conjunction",
 });
 
-export let serverBuildTargetWarning = `The "serverBuildTarget" config option is deprecated. Use a combination of "publicPath", "serverBuildPath", "serverConditions", "serverDependenciesToBundle", "serverMainFields", "serverMinify", "serverModuleFormat" and/or "serverPlatform" instead.`;
+export let serverBuildTargetWarning = `⚠️ DEPRECATED: The "serverBuildTarget" config option is deprecated. Use a combination of "publicPath", "serverBuildPath", "serverConditions", "serverDependenciesToBundle", "serverMainFields", "serverMinify", "serverModuleFormat" and/or "serverPlatform" instead.`;
+
+export let flatRoutesWarning = `⚠️ DEPRECATED: The old nested folders route convention has been deprecated in favor of "flat routes".  Please enable the new routing convention via the \`future.v2_routeConvention\` flag in your \`remix.config.js\` file.  For more information, please see https://remix.run/docs/en/main/file-conventions/route-files-v2.`;