diff --git a/.changeset/serious-berries-pretend.md b/.changeset/serious-berries-pretend.md
new file mode 100644
index 0000000000..5d871d63b9
--- /dev/null
+++ b/.changeset/serious-berries-pretend.md
@@ -0,0 +1,5 @@
+---
+"@react-router/dev": patch
+---
+
+avoid duplicate stylesheet links in framework mode when parent/layout routes and suspended child routes reference the same dynamic CSS asset, while preserving leaf-route dynamic CSS retention behavior
diff --git a/integration/vite-css-suspended-duplicate-test.ts b/integration/vite-css-suspended-duplicate-test.ts
new file mode 100644
index 0000000000..41244b0db5
--- /dev/null
+++ b/integration/vite-css-suspended-duplicate-test.ts
@@ -0,0 +1,177 @@
+import { test, expect } from "@playwright/test";
+import getPort from "get-port";
+
+import {
+  build,
+  createEditor,
+  createProject,
+  reactRouterServe,
+  viteConfig,
+} from "./helpers/vite.js";
+
+const js = String.raw;
+
+test.describe("Vite CSS suspended duplicate styles", () => {
+  let port: number;
+  let cwd: string;
+  let stop: () => void;
+
+  test.beforeAll(async () => {
+    port = await getPort();
+    cwd = await createProject(
+      {
+        "vite.config.ts": await viteConfig.basic({
+          port,
+          templateName: "vite-6-template",
+          vanillaExtract: true,
+        }),
+        "app/routes.ts": js`
+          import { type RouteConfig, index, route } from "@react-router/dev/routes";
+
+          export default [
+            route(":slug", "routes/$slug/layout.tsx", [
+              index("routes/$slug/route.tsx"),
+            ]),
+          ] satisfies RouteConfig;
+        `,
+        "app/components/WithStyles.css.ts": js`
+          import { style } from "@vanilla-extract/css";
+
+          export const withStyles = style({
+            color: "rgb(255, 0, 0)",
+          });
+        `,
+        "app/components/WithStyles.tsx": js`
+          import * as styles from "./WithStyles.css";
+
+          export function WithStyles() {
+            return <div data-with-styles className={styles.withStyles}>with styles</div>;
+          }
+        `,
+        "app/components/Suspended.tsx": js`
+          import { WithStyles } from "./WithStyles";
+
+          export function Suspended() {
+            return <WithStyles />;
+          }
+        `,
+        "app/routes/$slug/layout.tsx": js`
+          import { lazy, Suspense } from "react";
+          import { Outlet } from "react-router";
+
+          const SuspendedLazy = lazy(() =>
+            import("../../components/Suspended").then(({ Suspended }) => ({
+              default: Suspended,
+            })),
+          );
+
+          import { WithStyles } from "../../components/WithStyles";
+
+          export default function LayoutRoute() {
+            return (
+              <>
+                <h1 data-layout>layout</h1>
+                <Suspense fallback={"loading-layout"}>
+                  <SuspendedLazy />
+                </Suspense>
+                <Outlet />
+              </>
+            );
+          }
+        `,
+        "app/routes/$slug/route.tsx": js`
+          import { lazy, Suspense } from "react";
+
+          const SuspendedLazy = lazy(() =>
+            import("../../components/Suspended").then(({ Suspended }) => ({
+              default: Suspended,
+            })),
+          );
+
+          export default function SlugIndexRoute() {
+            return (
+              <>
+                <h2 data-route>route</h2>
+                <Suspense fallback={"loading-route"}>
+                  <SuspendedLazy />
+                </Suspense>
+              </>
+            );
+          }
+        `,
+      },
+      "vite-6-template",
+    );
+
+    let edit = createEditor(cwd);
+    await edit("package.json", (contents) =>
+      contents.replace('"sideEffects": false', '"sideEffects": true'),
+    );
+
+    let { status } = build({ cwd });
+    expect(status).toBe(0);
+    stop = await reactRouterServe({ cwd, port });
+  });
+
+  test.afterAll(() => stop());
+
+  test("does not duplicate stylesheet links for suspended components in nested routes", async ({
+    page,
+  }) => {
+    let stylesheetRequests: string[] = [];
+    page.on("requestfinished", (request) => {
+      if (request.resourceType() === "stylesheet") {
+        stylesheetRequests.push(request.url());
+      }
+    });
+
+    await page.goto(`http://localhost:${port}/some`, {
+      waitUntil: "networkidle",
+    });
+
+    await expect(page.locator("[data-layout]")).toHaveText("layout");
+    await expect(page.locator("[data-route]")).toHaveText("route");
+    await expect(page.locator("[data-with-styles]").first()).toHaveCSS(
+      "color",
+      "rgb(255, 0, 0)",
+    );
+
+    let stylesheetHrefs = await page.evaluate(() =>
+      Array.from(
+        document.querySelectorAll<HTMLLinkElement>("link[rel='stylesheet']"),
+      )
+        .map((link) => link.getAttribute("href"))
+        .filter((href): href is string => href != null),
+    );
+
+    let normalizeHref = (href: string) => href.replace(/#$/, "");
+    let normalizedLinkHrefs = stylesheetHrefs
+      .map(normalizeHref)
+      .filter((href) => href.includes("WithStyles.css.ts-"));
+    let normalizedRequestHrefs = stylesheetRequests.map((requestUrl) => {
+      let url = new URL(requestUrl);
+      return normalizeHref(url.pathname + url.search + url.hash);
+    })
+      .filter((href) => href.includes("WithStyles.css.ts-"));
+
+    let duplicateLinkHrefs = normalizedLinkHrefs.filter(
+      (href, index, hrefs) => hrefs.indexOf(href) !== index,
+    );
+    let duplicateRequestHrefs = normalizedRequestHrefs.filter(
+      (href, index, hrefs) => hrefs.indexOf(href) !== index,
+    );
+
+    expect(normalizedLinkHrefs.length).toBeGreaterThan(0);
+    expect(
+      duplicateLinkHrefs,
+      `Duplicate stylesheet links found.\nraw=${JSON.stringify(stylesheetHrefs)}\nnormalized=${JSON.stringify(normalizedLinkHrefs)}`,
+    ).toEqual([]);
+
+    if (normalizedRequestHrefs.length > 0) {
+      expect(
+        duplicateRequestHrefs,
+        `Duplicate stylesheet requests found.\nraw=${JSON.stringify(stylesheetRequests)}\nnormalized=${JSON.stringify(normalizedRequestHrefs)}`,
+      ).toEqual([]);
+    }
+  });
+});
diff --git a/packages/react-router-dev/vite/plugin.ts b/packages/react-router-dev/vite/plugin.ts
index 6eaf1297a3..ef4ab3a4f2 100644
--- a/packages/react-router-dev/vite/plugin.ts
+++ b/packages/react-router-dev/vite/plugin.ts
@@ -358,6 +358,13 @@ const getReactRouterManifestBuildAssets = (
   invariant(entryChunk, `Chunk not found: ${entryFilePath}`);
 
   let isRootRoute = Boolean(route && route.parentId === undefined);
+  // Keep `#` only for leaf routes to preserve dynamic-import CSS retention
+  // without duplicating parent/layout route styles.
+  let shouldUseForciblyUniqueCssHrefs =
+    route !== null &&
+    !Object.values(ctx.reactRouterConfig.routes).some(
+      (candidateRoute) => candidateRoute.parentId === route.id,
+    );
 
   let routeModuleChunks = routeChunkNames
     .map((routeChunkName) =>
@@ -413,7 +420,10 @@ const getReactRouterManifestBuildAssets = (
             // route-level CSS is removed from the document. We use a hash here
             // because it's a unique `href` value but isn't a unique network
             // request and only adds a single character.
-            return allDynamicCssFiles.has(href) ? `${publicHref}#` : publicHref;
+            return allDynamicCssFiles.has(href) &&
+              shouldUseForciblyUniqueCssHrefs
+              ? `${publicHref}#`
+              : publicHref;
           }),
       ]
         .flat(1)