From c9ff56ec74393373dbe0f58c3e24d1846b469317 Mon Sep 17 00:00:00 2001
From: "Sebastian \"Sebbie\" Silbermann" <sebastian.silbermann@vercel.com>
Date: Wed, 4 Feb 2026 10:56:33 +0100
Subject: [PATCH] [DevTools] Disable Activity slices by default (#35685)

---
 .../src/config/DevToolsFeatureFlags.core-fb.js                 | 1 +
 .../src/config/DevToolsFeatureFlags.core-oss.js                | 1 +
 .../src/config/DevToolsFeatureFlags.default.js                 | 1 +
 .../src/config/DevToolsFeatureFlags.extension-fb.js            | 1 +
 .../src/config/DevToolsFeatureFlags.extension-oss.js           | 1 +
 .../src/devtools/views/SuspenseTab/SuspenseTab.js              | 3 ++-
 6 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-fb.js b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-fb.js
index 9cec3ce338..5d9c476b3b 100644
--- a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-fb.js
+++ b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-fb.js
@@ -13,6 +13,7 @@
  * It should always be imported from "react-devtools-feature-flags".
  ************************************************************************/
 
+export const enableActivitySlices: boolean = false;
 export const enableLogger: boolean = true;
 export const enableStyleXFeatures: boolean = true;
 export const isInternalFacebookBuild: boolean = true;
diff --git a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-oss.js b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-oss.js
index 326b0fd16c..88b01afc3e 100644
--- a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-oss.js
+++ b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-oss.js
@@ -13,6 +13,7 @@
  * It should always be imported from "react-devtools-feature-flags".
  ************************************************************************/
 
+export const enableActivitySlices: boolean = __DEV__;
 export const enableLogger: boolean = false;
 export const enableStyleXFeatures: boolean = false;
 export const isInternalFacebookBuild: boolean = false;
diff --git a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.default.js b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.default.js
index e7355f8a34..85f678a980 100644
--- a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.default.js
+++ b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.default.js
@@ -13,6 +13,7 @@
  * It should always be imported from "react-devtools-feature-flags".
  ************************************************************************/
 
+export const enableActivitySlices: boolean = __DEV__;
 export const enableLogger: boolean = false;
 export const enableStyleXFeatures: boolean = false;
 export const isInternalFacebookBuild: boolean = false;
diff --git a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-fb.js b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-fb.js
index dc4f05d16f..734e7988c8 100644
--- a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-fb.js
+++ b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-fb.js
@@ -13,6 +13,7 @@
  * It should always be imported from "react-devtools-feature-flags".
  ************************************************************************/
 
+export const enableActivitySlices: boolean = false;
 export const enableLogger: boolean = true;
 export const enableStyleXFeatures: boolean = true;
 export const isInternalFacebookBuild: boolean = true;
diff --git a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-oss.js b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-oss.js
index 71df63eef0..c9b665a909 100644
--- a/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-oss.js
+++ b/packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-oss.js
@@ -13,6 +13,7 @@
  * It should always be imported from "react-devtools-feature-flags".
  ************************************************************************/
 
+export const enableActivitySlices: boolean = __DEV__;
 export const enableLogger: boolean = false;
 export const enableStyleXFeatures: boolean = false;
 export const isInternalFacebookBuild: boolean = false;
diff --git a/packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseTab.js b/packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseTab.js
index bd5de7d13e..0b195a99c4 100644
--- a/packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseTab.js
+++ b/packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseTab.js
@@ -16,6 +16,7 @@ import {
   Fragment,
 } from 'react';
 
+import {enableActivitySlices} from 'react-devtools-feature-flags';
 import {
   localStorageGetItem,
   localStorageSetItem,
@@ -284,7 +285,7 @@ function SuspenseTab(_: {}) {
   const {activities} = useContext(TreeStateContext);
   // If there are no named Activity boundaries, we don't have any tree list and we should hide
   // both the panel and the button to toggle it.
-  const activityListDisabled = activities.length === 0;
+  const activityListDisabled = !enableActivitySlices || activities.length === 0;
 
   const wrapperTreeRef = useRef<null | HTMLElement>(null);
   const resizeTreeRef = useRef<null | HTMLElement>(null);