diff --git a/packages/next/src/client/components/react-dev-overlay/app/app-dev-overlay.tsx b/packages/next/src/client/components/react-dev-overlay/app/app-dev-overlay.tsx
index bb1b74b51ea4..80110ed2b045 100644
--- a/packages/next/src/client/components/react-dev-overlay/app/app-dev-overlay.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/app/app-dev-overlay.tsx
@@ -72,6 +72,11 @@ function ReplaySsrOnlyErrors({
   return null
 }
 
+function getSquashedHydrationErrorDetails() {
+  // We don't squash hydration errors in the App Router.
+  return null
+}
+
 export function AppDevOverlay({
   state,
   dispatch,
@@ -99,7 +104,11 @@ export function AppDevOverlay({
       <>
         {/* Fonts can only be loaded outside the Shadow DOM. */}
         <FontStyles />
-        <DevOverlay state={state} dispatch={dispatch} />
+        <DevOverlay
+          state={state}
+          dispatch={dispatch}
+          getSquashedHydrationErrorDetails={getSquashedHydrationErrorDetails}
+        />
       </>
     </>
   )
diff --git a/packages/next/src/client/components/react-dev-overlay/pages/hydration-error-state.ts b/packages/next/src/client/components/react-dev-overlay/pages/hydration-error-state.ts
index 85919f946f08..1529529ce928 100644
--- a/packages/next/src/client/components/react-dev-overlay/pages/hydration-error-state.ts
+++ b/packages/next/src/client/components/react-dev-overlay/pages/hydration-error-state.ts
@@ -8,7 +8,7 @@ import {
   isErrorMessageWithComponentStackDiff as isReact19HydrationWarning,
 } from '../../react-19-hydration-error'
 
-type HydrationErrorState = {
+export type HydrationErrorState = {
   // Hydration warning template format: <message> <serverContent> <clientContent>
   warning?: string
   reactOutputComponentDiff?: string
diff --git a/packages/next/src/client/components/react-dev-overlay/pages/pages-dev-overlay.tsx b/packages/next/src/client/components/react-dev-overlay/pages/pages-dev-overlay.tsx
index f27060928a7d..5709bd316ad5 100644
--- a/packages/next/src/client/components/react-dev-overlay/pages/pages-dev-overlay.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/pages/pages-dev-overlay.tsx
@@ -2,6 +2,7 @@ import { PagesDevOverlayErrorBoundary } from './pages-dev-overlay-error-boundary
 import { usePagesDevOverlay } from './hooks'
 import { FontStyles } from '../font/font-styles'
 import { DevOverlay } from '../ui/dev-overlay'
+import { getSquashedHydrationErrorDetails } from './hydration-error-state'
 
 export type ErrorType = 'runtime' | 'build'
 
@@ -22,7 +23,11 @@ export function PagesDevOverlay({ children }: PagesDevOverlayProps) {
 
       {/* Fonts can only be loaded outside the Shadow DOM. */}
       <FontStyles />
-      <DevOverlay state={state} dispatch={dispatch} />
+      <DevOverlay
+        state={state}
+        dispatch={dispatch}
+        getSquashedHydrationErrorDetails={getSquashedHydrationErrorDetails}
+      />
     </>
   )
 }
diff --git a/packages/next/src/client/components/react-dev-overlay/ui/components/errors/error-overlay/error-overlay.tsx b/packages/next/src/client/components/react-dev-overlay/ui/components/errors/error-overlay/error-overlay.tsx
index 150fc2820569..a6593902c3ca 100644
--- a/packages/next/src/client/components/react-dev-overlay/ui/components/errors/error-overlay/error-overlay.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/ui/components/errors/error-overlay/error-overlay.tsx
@@ -9,6 +9,7 @@ import { BuildError } from '../../../container/build-error'
 import { Errors } from '../../../container/errors'
 import { useDelayedRender } from '../../../hooks/use-delayed-render'
 import type { ReadyRuntimeError } from '../../../../utils/get-error-by-type'
+import type { HydrationErrorState } from '../../../../pages/hydration-error-state'
 
 const transitionDurationMs = 200
 
@@ -23,11 +24,13 @@ export interface ErrorBaseProps {
 export function ErrorOverlay({
   state,
   dispatch,
+  getSquashedHydrationErrorDetails,
   runtimeErrors,
   errorCount,
 }: {
   state: OverlayState
   dispatch: OverlayDispatch
+  getSquashedHydrationErrorDetails: (error: Error) => HydrationErrorState | null
   runtimeErrors: ReadyRuntimeError[]
   errorCount: number
 }) {
@@ -74,6 +77,7 @@ export function ErrorOverlay({
     <Errors
       {...commonProps}
       debugInfo={state.debugInfo}
+      getSquashedHydrationErrorDetails={getSquashedHydrationErrorDetails}
       runtimeErrors={runtimeErrors}
       onClose={() => {
         dispatch({ type: ACTION_ERROR_OVERLAY_CLOSE })
diff --git a/packages/next/src/client/components/react-dev-overlay/ui/container/errors.tsx b/packages/next/src/client/components/react-dev-overlay/ui/container/errors.tsx
index 3b8257e9b39d..70031ee92ab2 100644
--- a/packages/next/src/client/components/react-dev-overlay/ui/container/errors.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/ui/container/errors.tsx
@@ -17,9 +17,10 @@ import {
 } from '../../../react-19-hydration-error'
 import type { ReadyRuntimeError } from '../../utils/get-error-by-type'
 import type { ErrorBaseProps } from '../components/errors/error-overlay/error-overlay'
-import { getSquashedHydrationErrorDetails } from '../../pages/hydration-error-state'
+import type { HydrationErrorState } from '../../pages/hydration-error-state'
 
 export interface ErrorsProps extends ErrorBaseProps {
+  getSquashedHydrationErrorDetails: (error: Error) => HydrationErrorState | null
   runtimeErrors: ReadyRuntimeError[]
   debugInfo: DebugInfo
   onClose: () => void
@@ -72,7 +73,10 @@ const noErrorDetails = {
   notes: null,
   reactOutputComponentDiff: null,
 }
-function useErrorDetails(error: Error | undefined): {
+function useErrorDetails(
+  error: Error | undefined,
+  getSquashedHydrationErrorDetails: (error: Error) => HydrationErrorState | null
+): {
   hydrationWarning: string | null
   notes: string | null
   reactOutputComponentDiff: string | null
@@ -106,10 +110,11 @@ function useErrorDetails(error: Error | undefined): {
       notes,
       reactOutputComponentDiff: diff,
     }
-  }, [error])
+  }, [error, getSquashedHydrationErrorDetails])
 }
 
 export function Errors({
+  getSquashedHydrationErrorDetails,
   runtimeErrors,
   debugInfo,
   onClose,
@@ -127,7 +132,10 @@ export function Errors({
     () => runtimeErrors[activeIdx] ?? null,
     [activeIdx, runtimeErrors]
   )
-  const errorDetails = useErrorDetails(activeError?.error)
+  const errorDetails = useErrorDetails(
+    activeError?.error,
+    getSquashedHydrationErrorDetails
+  )
 
   if (isLoading) {
     // TODO: better loading state
diff --git a/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.stories.tsx b/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.stories.tsx
index b3dababe5a51..ded4b633acf3 100644
--- a/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.stories.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.stories.tsx
@@ -102,6 +102,10 @@ function useOverlayReducer() {
   }, initialState)
 }
 
+function getNoSquashedHydrationErrorDetails() {
+  return null
+}
+
 export const Default: Story = {
   render: function DevOverlayStory() {
     const [state, dispatch] = useOverlayReducer()
@@ -115,7 +119,14 @@ export const Default: Story = {
             objectFit: 'contain',
           }}
         />
-        <DevOverlay state={state} dispatch={dispatch} />
+        <DevOverlay
+          state={state}
+          dispatch={dispatch}
+          getSquashedHydrationErrorDetails={
+            // Testing like App Router where we no longer quash hydration errors
+            getNoSquashedHydrationErrorDetails
+          }
+        />
       </>
     )
   },
diff --git a/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.tsx b/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.tsx
index 1bde4b5e491c..d5304ccad2e4 100644
--- a/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.tsx
+++ b/packages/next/src/client/components/react-dev-overlay/ui/dev-overlay.tsx
@@ -10,13 +10,16 @@ import { DevToolsIndicator } from './components/errors/dev-tools-indicator/dev-t
 import { RenderError } from './container/runtime-error/render-error'
 import { DarkTheme } from './styles/dark-theme'
 import { useDevToolsScale } from './components/errors/dev-tools-indicator/dev-tools-info/preferences'
+import type { HydrationErrorState } from '../pages/hydration-error-state'
 
 export function DevOverlay({
   state,
   dispatch,
+  getSquashedHydrationErrorDetails,
 }: {
   state: OverlayState
   dispatch: OverlayDispatch
+  getSquashedHydrationErrorDetails: (error: Error) => HydrationErrorState | null
 }) {
   const [scale, setScale] = useDevToolsScale()
   return (
@@ -46,6 +49,9 @@ export function DevOverlay({
               <ErrorOverlay
                 state={state}
                 dispatch={dispatch}
+                getSquashedHydrationErrorDetails={
+                  getSquashedHydrationErrorDetails
+                }
                 runtimeErrors={runtimeErrors}
                 errorCount={totalErrorCount}
               />