diff --git a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
index 10806e41f2141..77ca9da4e649d 100644
--- a/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
+++ b/packages/shared/forks/ReactFeatureFlags.www-dynamic.js
@@ -34,6 +34,16 @@ export const enableDebugTracing = __EXPERIMENTAL__;
 
 export const enableSchedulingProfiler = __VARIANT__;
 
+// This only has an effect in the new reconciler. But also, the new reconciler
+// is only enabled when __VARIANT__ is true. So this is set to the opposite of
+// __VARIANT__ so that it's `false` when running against the new reconciler.
+// Ideally we would test both against the new reconciler, but until then, we
+// should test the value that is used in www. Which is `false`.
+//
+// Once Lanes has landed in both reconciler forks, we'll get coverage of
+// both branches.
+export const deferRenderPhaseUpdateToNextBatch = !__VARIANT__;
+
 // These are already tested in both modes using the build type dimension,
 // so we don't need to use __VARIANT__ to get extra coverage.
 export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
diff --git a/packages/shared/forks/ReactFeatureFlags.www.js b/packages/shared/forks/ReactFeatureFlags.www.js
index 69770109ce8c0..1861d00a2dcb2 100644
--- a/packages/shared/forks/ReactFeatureFlags.www.js
+++ b/packages/shared/forks/ReactFeatureFlags.www.js
@@ -22,6 +22,7 @@ export const {
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
   enableFilterEmptyStringAttributesDOM,
   enableLegacyFBSupport,
+  deferRenderPhaseUpdateToNextBatch,
   enableDebugTracing,
   skipUnmountedBoundaries,
   enableUseRefAccessWarning,
@@ -45,7 +46,6 @@ export const enableProfilerNestedUpdateScheduledHook: boolean =
 export const enableUpdaterTracking = __PROFILE__;
 
 export const createRootStrictEffectsByDefault = false;
-export const deferRenderPhaseUpdateToNextBatch = false;
 export const enableSuspenseAvoidThisFallback = true;
 export const enableSuspenseAvoidThisFallbackFizz = false;
 export const enableCPUSuspense = true;