diff --git a/docs/content/2.module/1.utils-kit.md b/docs/content/2.module/1.utils-kit.md
index d84ce740c3..b7902c9f68 100644
--- a/docs/content/2.module/1.utils-kit.md
+++ b/docs/content/2.module/1.utils-kit.md
@@ -233,6 +233,28 @@ export const devtoolsClient = useDevtoolsClient()
 
 When the iframe been served with the same origin (CORS limitation), devtools will automatically inject `__NUXT_DEVTOOLS__` to the iframe's window object. You can access it as a ref using `useDevtoolsClient()` utility.
 
+### `onDevtoolsReady()`
+
+The client-side mirror of the server's [`onDevtoolsReady`](#ondevtoolsready). The
+callback runs once the Vite DevTools client is connected and receives the
+`DevToolsRpcClient` (the same object as `client.devtools.devtoolsKit`), giving
+full devframe-native access. This is the recommended way to register client RPC
+functions:
+
+```ts
+import { onDevtoolsReady } from '@nuxt/devtools-kit/iframe-client'
+
+onDevtoolsReady((kit) => {
+  kit.client.register({
+    name: 'my-module:on-update',
+    type: 'event',
+    handler: (payload) => {
+      // ...
+    },
+  })
+})
+```
+
 ### `useDevtoolsClient()`
 
 It will return a ref of `NuxtDevtoolsIframeClient` object that are intially `null` and will be updated when the connection is ready.
@@ -250,6 +272,24 @@ For example, you can get the router instance from the client app:
 const router = computed(() => devtoolsClient.value?.host?.nuxt.vueApp.config.globalProperties?.$router)
 ```
 
+The `devtools` object also exposes `devtoolsKit` — the connected Vite DevTools
+RPC client (mirroring `nuxt.devtools.devtoolsKit` on the server) — for full
+devframe-native access. Use it to register client RPC functions, call server
+functions, and more:
+
+```ts
+const kit = devtoolsClient.value?.devtools.devtoolsKit
+kit?.client.register({
+  name: 'my-module:on-update',
+  type: 'event',
+  handler: (payload) => {
+    // ...
+  },
+})
+```
+
+This replaces the deprecated `devtools.extendClientRpc()`.
+
 ### `onDevtoolsClientConnected()`
 
 Similiar to `useDevtoolsClient()` but as a callback style:
diff --git a/packages/devtools-kit/src/_types/client-api.ts b/packages/devtools-kit/src/_types/client-api.ts
index 9ac2b14e04..c260cfa7f1 100644
--- a/packages/devtools-kit/src/_types/client-api.ts
+++ b/packages/devtools-kit/src/_types/client-api.ts
@@ -1,4 +1,5 @@
 import type {} from '@nuxt/schema'
+import type { DevToolsRpcClient } from '@vitejs/devtools-kit/client'
 import type { Hookable } from 'hookable'
 import type { NuxtApp } from 'nuxt/app'
 import type { AppConfig } from 'nuxt/schema'
@@ -118,6 +119,21 @@ export interface NuxtDevtoolsClient {
   renderMarkdown: (markdown: string) => string
   colorMode: string
 
+  /**
+   * The connected Vite DevTools RPC client, mirroring `nuxt.devtools.devtoolsKit`
+   * on the server. Use it for full devframe-native access — register client RPC
+   * functions (`devtoolsKit.client.register(...)`), call server functions
+   * (`devtoolsKit.call(...)`), shared state, streaming, scoping, etc.
+   *
+   * `undefined` until the DevTools client has connected.
+   */
+  devtoolsKit: DevToolsRpcClient | undefined
+
+  /**
+   * @deprecated Use `onDevtoolsReady((kit) => kit.client.register(...))` from
+   * `@nuxt/devtools-kit/iframe-client`, or the exposed `devtoolsKit` client
+   * directly (`client.devtools.devtoolsKit?.client.register(...)`).
+   */
   extendClientRpc: <ServerFunctions extends object = Record<string, unknown>, ClientFunctions extends object = Record<string, unknown>>(name: string, functions: ClientFunctions) => ServerFunctions
 }
 
diff --git a/packages/devtools-kit/src/runtime/iframe-client.ts b/packages/devtools-kit/src/runtime/iframe-client.ts
index ecc4183275..571647babf 100644
--- a/packages/devtools-kit/src/runtime/iframe-client.ts
+++ b/packages/devtools-kit/src/runtime/iframe-client.ts
@@ -1,3 +1,4 @@
+import type { DevToolsRpcClient } from '@vitejs/devtools-kit/client'
 import type { Ref } from 'vue'
 import type { NuxtDevtoolsIframeClient } from '../types'
 import { shallowRef, triggerRef } from 'vue'
@@ -39,6 +40,30 @@ export function onDevtoolsClientConnected(fn: (client: NuxtDevtoolsIframeClient)
   }
 }
 
+/**
+ * Run a callback once the Vite DevTools client is ready, receiving the connected
+ * `DevToolsRpcClient` — the client-side mirror of the server's
+ * `onDevtoolsReady((ctx) => …)`.
+ *
+ * This is the recommended way to do client-side DevTools integration (register
+ * client RPC functions, call server functions, shared state, streaming, …):
+ *
+ * ```ts
+ * import { onDevtoolsReady } from '@nuxt/devtools-kit/iframe-client'
+ *
+ * onDevtoolsReady((kit) => {
+ *   kit.client.register({ name: 'my-module:on-update', type: 'event', handler })
+ * })
+ * ```
+ */
+export function onDevtoolsReady(fn: (kit: DevToolsRpcClient) => void) {
+  return onDevtoolsClientConnected((client) => {
+    const kit = client.devtools.devtoolsKit
+    if (kit)
+      fn(kit)
+  })
+}
+
 export function useDevtoolsClient() {
   if (!clientRef) {
     clientRef = shallowRef<NuxtDevtoolsIframeClient | undefined>()
diff --git a/packages/devtools/client/composables/client.ts b/packages/devtools/client/composables/client.ts
index 85b932288a..be8a75f6be 100644
--- a/packages/devtools/client/composables/client.ts
+++ b/packages/devtools/client/composables/client.ts
@@ -10,6 +10,21 @@ import { renderMarkdown } from './client-services/markdown'
 import { renderCodeHighlight } from './client-services/shiki'
 import { connectPromise, rpc, rpcClient, upsertClientFunction } from './rpc'
 
+let warnedExtendClientRpc = false
+/**
+ * @deprecated `extendClientRpc` is deprecated. Use `onDevtoolsReady` from
+ * `@nuxt/devtools-kit/iframe-client`, or the exposed `devtoolsKit` client.
+ */
+function warnExtendClientRpcDeprecated() {
+  if (warnedExtendClientRpc)
+    return
+  warnedExtendClientRpc = true
+  console.warn(
+    '[nuxt-devtools] `extendClientRpc` is deprecated. Use `onDevtoolsReady((kit) => '
+    + 'kit.client.register(...))` from `@nuxt/devtools-kit/iframe-client`.',
+  )
+}
+
 export function useClient() {
   return useState<NuxtDevtoolsHostClient>('devtools-client')
 }
@@ -52,6 +67,7 @@ export function useInjectionClient(): ComputedRef<NuxtDevtoolsIframeClient> {
     host: client.value,
     devtools: <NuxtDevtoolsClient>{
       rpc,
+      devtoolsKit: rpcClient.value,
       colorMode: mode.value,
       renderCodeHighlight(code, lang) {
         return renderCodeHighlight(code, lang as any)
@@ -60,9 +76,11 @@ export function useInjectionClient(): ComputedRef<NuxtDevtoolsIframeClient> {
         return renderMarkdown(code)
       },
       extendClientRpc(namespace, functions) {
+        warnExtendClientRpcDeprecated()
         const register = (client: DevToolsRpcClient) => {
           for (const [name, handler] of Object.entries(functions)) {
             if (typeof handler === 'function')
+              // force-registers (override by default) via upsertClientFunction
               upsertClientFunction(client, `${namespace}:${name}`, handler as any)
           }
         }
diff --git a/packages/devtools/client/composables/rpc.ts b/packages/devtools/client/composables/rpc.ts
index 5e58ef3898..367caddda9 100644
--- a/packages/devtools/client/composables/rpc.ts
+++ b/packages/devtools/client/composables/rpc.ts
@@ -77,13 +77,16 @@ export async function registerClientFunctions() {
  * Register (or replace) a client-side event function on the devframe RPC host.
  *
  * devframe 0.6 split registration into `register()` (throws DF0021 if the name
- * already exists) and `update()` (throws DF0022 if it does not), so pick the
- * right one based on the current definitions to keep this an idempotent upsert.
+ * already exists) and `update()` (throws DF0022 if it does not). We always
+ * force-register so this stays an idempotent override regardless of the current
+ * state — the client re-runs registration on (re)connect and integrations may
+ * override a function, so neither error should ever surface.
  */
 export function upsertClientFunction(client: DevToolsRpcClient, name: string, handler: (...args: any[]) => any) {
   const definition = { name, type: 'event', handler } as const
-  if (client.client.definitions.has(name))
-    client.client.update(definition as any)
-  else
-    client.client.register(definition as any)
+  // The cast is a workaround for a devframe type gap: its `RpcFunctionsCollector`
+  // interface (used for the client host) omits the `force` parameter that the
+  // concrete `RpcFunctionsCollectorBase` and the runtime actually accept. Drop
+  // the cast once devframe types `register(fn, force?)` on the interface.
+  ;(client.client.register as (fn: any, force?: boolean) => void)(definition, true)
 }