diff --git a/packages/react-reconciler/src/ReactFiber.old.js b/packages/react-reconciler/src/ReactFiber.old.js
index 90d0d7a7ac6fa..b26509f25d139 100644
--- a/packages/react-reconciler/src/ReactFiber.old.js
+++ b/packages/react-reconciler/src/ReactFiber.old.js
@@ -771,6 +771,7 @@ export function createFiberFromTracingMarker(
   const tracingMarkerInstance: TracingMarkerInstance = {
     transitions: null,
     pendingSuspenseBoundaries: null,
+    hasUpdate: false,
   };
   fiber.stateNode = tracingMarkerInstance;
   return fiber;
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.old.js b/packages/react-reconciler/src/ReactFiberBeginWork.old.js
index a4fccc0bbd73d..ac501c2e9218b 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.old.js
@@ -909,6 +909,7 @@ function updateTracingMarkerComponent(
       const markerInstance: TracingMarkerInstance = {
         transitions: new Set(currentTransitions),
         pendingSuspenseBoundaries: new Map(),
+        hasUpdate: false,
       };
       workInProgress.stateNode = markerInstance;
     }
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.old.js b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
index eae4bc52e3585..53b352fc185a9 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
@@ -138,6 +138,7 @@ import {
   enqueuePendingPassiveProfilerEffect,
   restorePendingUpdaters,
   addTransitionStartCallbackToPendingTransition,
+  addTransitionProgressCallbackToPendingTransition,
   addTransitionCompleteCallbackToPendingTransition,
   addMarkerCompleteCallbackToPendingTransition,
   setIsRunningInsertionEffect,
@@ -1110,10 +1111,17 @@ function commitTransitionProgress(offscreenFiber: Fiber) {
       // The suspense boundaries was just hidden. Add the boundary
       // to the pending boundary set if it's there
       if (pendingMarkers !== null) {
-        pendingMarkers.forEach(pendingBoundaries => {
-          pendingBoundaries.set(offscreenInstance, {
-            name,
-          });
+        pendingMarkers.forEach(markerInstance => {
+          const pendingBoundaries = markerInstance.pendingSuspenseBoundaries;
+          if (
+            pendingBoundaries !== null &&
+            !pendingBoundaries.has(offscreenInstance)
+          ) {
+            pendingBoundaries.set(offscreenInstance, {
+              name,
+            });
+            markerInstance.hasUpdate = true;
+          }
         });
       }
     } else if (wasHidden && !isHidden) {
@@ -1121,9 +1129,14 @@ function commitTransitionProgress(offscreenFiber: Fiber) {
       // the boundary from the pending suspense boundaries set
       // if it's there
       if (pendingMarkers !== null) {
-        pendingMarkers.forEach(pendingBoundaries => {
-          if (pendingBoundaries.has(offscreenInstance)) {
+        pendingMarkers.forEach(markerInstance => {
+          const pendingBoundaries = markerInstance.pendingSuspenseBoundaries;
+          if (
+            pendingBoundaries !== null &&
+            pendingBoundaries.has(offscreenInstance)
+          ) {
             pendingBoundaries.delete(offscreenInstance);
+            markerInstance.hasUpdate = true;
           }
         });
       }
@@ -2822,6 +2835,7 @@ function commitPassiveMountOnFiber(
           clearTransitionsForLanes(finishedRoot, committedLanes);
         }
 
+<<<<<<< HEAD
         incompleteTransitions.forEach(
           ({pendingSuspenseBoundaries}, transition) => {
             if (
@@ -2833,6 +2847,25 @@ function commitPassiveMountOnFiber(
             }
           },
         );
+=======
+        incompleteTransitions.forEach((markerInstance, transition) => {
+          const pendingBoundaries = markerInstance.pendingSuspenseBoundaries;
+          if (markerInstance.hasUpdate) {
+            addTransitionProgressCallbackToPendingTransition({
+              transition,
+              pending: pendingBoundaries || [],
+            });
+            markerInstance.hasUpdate = false;
+          }
+          if (pendingBoundaries === null || pendingBoundaries.size === 0) {
+            addTransitionCompleteCallbackToPendingTransition({
+              transitionName: transition.name,
+              startTime: transition.startTime,
+            });
+            incompleteTransitions.delete(transition);
+          }
+        });
+>>>>>>> 1f1184300 (old)
 
         clearTransitionsForLanes(finishedRoot, committedLanes);
       }
@@ -2900,10 +2933,25 @@ function commitPassiveMountOnFiber(
                 if (markerTransitions !== null) {
                   markerTransitions.forEach(transition => {
                     if (instance.transitions === null) {
+<<<<<<< HEAD
                       instance.transitions = new Set();
                     } else if (instance.transitions.has(transition)) {
                       if (markerInstance.pendingSuspenseBoundaries === null) {
                         markerInstance.pendingSuspenseBoundaries = new Map();
+=======
+                      // TODO: What if instance.transitions is null?
+                    } else {
+                      if (instance.transitions.has(transition)) {
+                        if (
+                          instance.pendingMarkers === null ||
+                          markerInstance.pendingSuspenseBoundaries === null
+                        ) {
+                          // TODO: What if instance.pendingMarkers is null?
+                          // TODO: What if markerInstance.pendingSuspenseBoundaries is null?
+                        } else {
+                          instance.pendingMarkers.add(markerInstance);
+                        }
+>>>>>>> 1f1184300 (old)
                       }
                       if (instance.pendingMarkers === null) {
                         instance.pendingMarkers = new Set();
diff --git a/packages/react-reconciler/src/ReactFiberTracingMarkerComponent.old.js b/packages/react-reconciler/src/ReactFiberTracingMarkerComponent.old.js
index 0aba8780968af..8629824e1b950 100644
--- a/packages/react-reconciler/src/ReactFiberTracingMarkerComponent.old.js
+++ b/packages/react-reconciler/src/ReactFiberTracingMarkerComponent.old.js
@@ -22,10 +22,24 @@ export type MarkerTransition = {
   name: string,
 };
 
+<<<<<<< HEAD
 export type PendingTransitionCallbacks = {
   transitionStart: Array<Transition> | null,
   transitionComplete: Array<Transition> | null,
   markerComplete: Array<MarkerTransition> | null,
+=======
+export type TransitionProgress = {
+  transition: Transition,
+  pending: PendingSuspenseBoundaries,
+};
+
+export type MarkerTransitionObject = TransitionObject & {markerName: string};
+export type PendingTransitionCallbacks = {
+  transitionStart: Array<TransitionObject> | null,
+  transitionProgress: Array<TransitionProgress> | null,
+  transitionComplete: Array<TransitionObject> | null,
+  markerComplete: Array<MarkerTransitionObject> | null,
+>>>>>>> 1f1184300 (old)
 };
 
 export type Transition = {
@@ -42,6 +56,7 @@ export type BatchConfigTransition = {
 export type TracingMarkerInstance = {|
   pendingSuspenseBoundaries: PendingSuspenseBoundaries | null,
   transitions: Set<Transition> | null,
+  hasUpdate: boolean,
 |};
 
 export type PendingSuspenseBoundaries = Map<OffscreenInstance, SuspenseInfo>;
@@ -76,6 +91,19 @@ export function processTransitionCallbacks(
         });
       }
 
+      const transitionProgress = pendingTransitions.transitionProgress;
+      const onTransitionProgress = callbacks.onTransitionProgress;
+      if (onTransitionProgress != null && transitionProgress !== null) {
+        transitionProgress.forEach(({transition, pending}) => {
+          onTransitionProgress(
+            transition.name,
+            transition.startTime,
+            endTime,
+            Array.from(pending.values()),
+          );
+        });
+      }
+
       const transitionComplete = pendingTransitions.transitionComplete;
       if (transitionComplete !== null) {
         transitionComplete.forEach(transition => {
@@ -117,10 +145,12 @@ export function pushRootMarkerInstance(workInProgress: Fiber): void {
     if (transitions !== null) {
       transitions.forEach(transition => {
         if (!root.incompleteTransitions.has(transition)) {
-          root.incompleteTransitions.set(transition, {
+          const markerInstance: TracingMarkerInstance = {
             transitions: new Set([transition]),
             pendingSuspenseBoundaries: null,
-          });
+            hasUpdate: true,
+          };
+          root.incompleteTransitions.set(transition, markerInstance);
         }
       });
     }
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
index 3d3a32d8c9d5d..29ff22a061523 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
@@ -17,7 +17,13 @@ import type {FunctionComponentUpdateQueue} from './ReactFiberHooks.old';
 import type {EventPriority} from './ReactEventPriorities.old';
 import type {
   PendingTransitionCallbacks,
+<<<<<<< HEAD
   MarkerTransition,
+=======
+  TransitionObject,
+  MarkerTransitionObject,
+  TransitionProgress,
+>>>>>>> 1f1184300 (old)
   Transition,
 } from './ReactFiberTracingMarkerComponent.old';
 
@@ -349,6 +355,7 @@ export function addTransitionStartCallbackToPendingTransition(
     if (currentPendingTransitionCallbacks === null) {
       currentPendingTransitionCallbacks = {
         transitionStart: [],
+        transitionProgress: null,
         transitionComplete: null,
         markerComplete: null,
       };
@@ -369,6 +376,7 @@ export function addMarkerCompleteCallbackToPendingTransition(
     if (currentPendingTransitionCallbacks === null) {
       currentPendingTransitionCallbacks = {
         transitionStart: null,
+        transitionProgress: null,
         transitionComplete: null,
         markerComplete: [],
       };
@@ -382,6 +390,27 @@ export function addMarkerCompleteCallbackToPendingTransition(
   }
 }
 
+export function addTransitionProgressCallbackToPendingTransition(
+  transition: TransitionProgress,
+) {
+  if (enableTransitionTracing) {
+    if (currentPendingTransitionCallbacks === null) {
+      currentPendingTransitionCallbacks = {
+        transitionStart: null,
+        transitionProgress: [],
+        transitionComplete: null,
+        markerComplete: null,
+      };
+    }
+
+    if (currentPendingTransitionCallbacks.transitionProgress === null) {
+      currentPendingTransitionCallbacks.transitionProgress = [];
+    }
+
+    currentPendingTransitionCallbacks.transitionProgress.push(transition);
+  }
+}
+
 export function addTransitionCompleteCallbackToPendingTransition(
   transition: Transition,
 ) {
@@ -389,6 +418,7 @@ export function addTransitionCompleteCallbackToPendingTransition(
     if (currentPendingTransitionCallbacks === null) {
       currentPendingTransitionCallbacks = {
         transitionStart: null,
+        transitionProgress: null,
         transitionComplete: [],
         markerComplete: null,
       };