diff --git a/packages/router-core/src/ssr/serializer/NotFoundErrorPlugin.ts b/packages/router-core/src/ssr/serializer/NotFoundErrorPlugin.ts
new file mode 100644
index 0000000000..5947d88e02
--- /dev/null
+++ b/packages/router-core/src/ssr/serializer/NotFoundErrorPlugin.ts
@@ -0,0 +1,81 @@
+import { createPlugin } from 'seroval'
+import type { SerovalNode } from 'seroval'
+
+interface NotFoundNode {
+  message: SerovalNode
+  routeId: SerovalNode
+  data: SerovalNode
+  global: SerovalNode
+  _global: SerovalNode
+}
+
+/**
+ * Serializes NotFoundError instances (objects with `isNotFound: true`) so that
+ * all router metadata (routeId, data, global, _global) survives SSR dehydration
+ * and client-side hydration.  This plugin must be registered before
+ * ShallowErrorPlugin because notFound() now returns an Error subclass – without
+ * this plugin ShallowErrorPlugin would match first and strip all custom
+ * properties, keeping only `message`.
+ */
+export const NotFoundErrorPlugin = /* @__PURE__ */ createPlugin<
+  any,
+  NotFoundNode
+>({
+  tag: '$TSR/NotFoundError',
+  test(value) {
+    return !!value?.isNotFound
+  },
+  parse: {
+    sync(value, ctx) {
+      return {
+        message: ctx.parse(value.message),
+        routeId: ctx.parse(value.routeId),
+        data: ctx.parse(value.data),
+        global: ctx.parse(value.global),
+        _global: ctx.parse(value._global),
+      }
+    },
+    async async(value, ctx) {
+      return {
+        message: await ctx.parse(value.message),
+        routeId: await ctx.parse(value.routeId),
+        data: await ctx.parse(value.data),
+        global: await ctx.parse(value.global),
+        _global: await ctx.parse(value._global),
+      }
+    },
+    stream(value, ctx) {
+      return {
+        message: ctx.parse(value.message),
+        routeId: ctx.parse(value.routeId),
+        data: ctx.parse(value.data),
+        global: ctx.parse(value.global),
+        _global: ctx.parse(value._global),
+      }
+    },
+  },
+  serialize(node, ctx) {
+    return (
+      'Object.assign(new Error(' +
+      ctx.serialize(node.message) +
+      '),{isNotFound:true,routeId:' +
+      ctx.serialize(node.routeId) +
+      ',data:' +
+      ctx.serialize(node.data) +
+      ',global:' +
+      ctx.serialize(node.global) +
+      ',_global:' +
+      ctx.serialize(node._global) +
+      '})'
+    )
+  },
+  deserialize(node, ctx) {
+    return Object.assign(new Error(ctx.deserialize(node.message) as string), {
+      isNotFound: true,
+      routeId: ctx.deserialize(node.routeId),
+      data: ctx.deserialize(node.data),
+      global: ctx.deserialize(node.global),
+      _global: ctx.deserialize(node._global),
+    })
+  },
+})
diff --git a/packages/router-core/src/ssr/serializer/seroval-plugins.ts b/packages/router-core/src/ssr/serializer/seroval-plugins.ts
index de10d3bdc0..7df43fc048 100644
--- a/packages/router-core/src/ssr/serializer/seroval-plugins.ts
+++ b/packages/router-core/src/ssr/serializer/seroval-plugins.ts
@@ -1,9 +1,14 @@
 import { ReadableStreamPlugin } from 'seroval-plugins/web'
+import { NotFoundErrorPlugin } from './NotFoundErrorPlugin'
 import { ShallowErrorPlugin } from './ShallowErrorPlugin'
 import { RawStreamSSRPlugin } from './RawStream'
 import type { Plugin } from 'seroval'
 
 export const defaultSerovalPlugins = [
+  // NotFoundErrorPlugin must come before ShallowErrorPlugin: notFound() now
+  // returns an Error instance, and ShallowErrorPlugin would otherwise match it
+  // first and strip all custom properties (isNotFound, routeId, data, etc.).
+  NotFoundErrorPlugin as Plugin<any, any>,
   ShallowErrorPlugin as Plugin<Error, any>,
   // RawStreamSSRPlugin must come before ReadableStreamPlugin to match first
   RawStreamSSRPlugin,