better-auth/examples/tanstack-example/app/router.tsx

import { createRouter as createTanStackRouter } from "@tanstack/react-router";
import { routeTree } from "./routeTree.gen";

export function createRouter() {
	const router = createTanStackRouter({
		routeTree,
	});

	return router;
}

declare module "@tanstack/react-router" {
	interface Register {
		router: ReturnType<typeof createRouter>;
	}
}