diff --git a/Source/IGListKit/IGListAdapterUpdater.m b/Source/IGListKit/IGListAdapterUpdater.m
index d2c10297..0c5e37a5 100644
--- a/Source/IGListKit/IGListAdapterUpdater.m
+++ b/Source/IGListKit/IGListAdapterUpdater.m
@@ -17,6 +17,8 @@
 #import "IGListReloadIndexPath.h"
 #import "UICollectionView+IGListBatchUpdateData.h"
 
+typedef void (^IGListAdapterUpdaterDiffResultBlock)(IGListIndexSetResult *);
+
 @implementation IGListAdapterUpdater
 
 - (instancetype)init {
@@ -112,6 +114,7 @@
     void (^objectTransitionBlock)(NSArray *) = [self.objectTransitionBlock copy];
     const BOOL animated = self.queuedUpdateIsAnimated;
     const BOOL allowsReloadingOnTooManyUpdates = self.allowsReloadingOnTooManyUpdates;
+    const IGListExperiment experiments = self.experiments;
     IGListBatchUpdates *batchUpdates = self.batchUpdates;
 
     // clean up all state so that new updates can be coalesced while the current update is in flight
@@ -197,12 +200,6 @@
         return;
     }
 
-    const IGListExperiment experiments = self.experiments;
-
-    IGListIndexSetResult *(^performDiff)(void) = ^{
-        return IGListDiffExperiment(fromObjects, toObjects, IGListDiffEquality, experiments);
-    };
-
     // block executed in the first param block of -[UICollectionView performBatchUpdates:completion:]
     void (^batchUpdatesBlock)(IGListIndexSetResult *result) = ^(IGListIndexSetResult *result){
         executeUpdateBlocks();
@@ -230,7 +227,7 @@
                                                                          experiments,
                                                                          self.movesAsDeletesInserts,
                                                                          self.preferItemReloadsForSectionReloads);
-}
+        }
 
         [self _cleanStateAfterUpdates];
         [self _performBatchUpdatesItemBlockApplied];
@@ -306,17 +303,12 @@ willPerformBatchUpdatesWithCollectionView:collectionView
         }
     };
 
-    if (IGListExperimentEnabled(experiments, IGListExperimentBackgroundDiffing)) {
-        dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
-            IGListIndexSetResult *result = performDiff();
-            dispatch_async(dispatch_get_main_queue(), ^{
-                tryToPerformUpdate(result);
-            });
-        });
-    } else {
-        IGListIndexSetResult *result = performDiff();
+    const BOOL onBackgroundThread = IGListExperimentEnabled(experiments, IGListExperimentBackgroundDiffing);
+    [delegate listAdapterUpdater:self willDiffFromObjects:fromObjects toObjects:toObjects];
+    IGListAdapterUpdaterPerformDiffing(fromObjects, toObjects, IGListDiffEquality, onBackgroundThread, experiments, ^(IGListIndexSetResult *result){
+        [delegate listAdapterUpdater:self didDiffWithResults:result onBackgroundThread:onBackgroundThread];
         tryToPerformUpdate(result);
-    }
+    });
 }
 
 - (void)_beginPerformBatchUpdatesToObjects:(NSArray *)toObjects {
@@ -374,7 +366,6 @@ willPerformBatchUpdatesWithCollectionView:collectionView
     });
 }
 
-
 #pragma mark - IGListUpdatingDelegate
 
 static BOOL IGListIsEqual(const void *a, const void *b, NSUInteger (*size)(const void *item)) {
@@ -575,5 +566,25 @@ static NSUInteger IGListIdentifierHash(const void *item, NSUInteger (*size)(cons
     }
 }
 
+#pragma mark - Diffing
+
+static void IGListAdapterUpdaterPerformDiffing(NSArray<id<IGListDiffable>> *_Nullable oldArray,
+                                               NSArray<id<IGListDiffable>> *_Nullable newArray,
+                                               IGListDiffOption option,
+                                               IGListExperiment experiments,
+                                               BOOL onBackgroundThread,
+                                               IGListAdapterUpdaterDiffResultBlock completion) {
+    if (onBackgroundThread) {
+        dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
+            IGListIndexSetResult *result = IGListDiffExperiment(oldArray, newArray, option, experiments);
+            dispatch_async(dispatch_get_main_queue(), ^{
+                completion(result);
+            });
+        });
+    } else {
+        IGListIndexSetResult *result = IGListDiffExperiment(oldArray, newArray, option, experiments);
+        completion(result);
+    }
+}
 
 @end
diff --git a/Source/IGListKit/IGListAdapterUpdaterDelegate.h b/Source/IGListKit/IGListAdapterUpdaterDelegate.h
index 0f9aee84..695875a5 100644
--- a/Source/IGListKit/IGListAdapterUpdaterDelegate.h
+++ b/Source/IGListKit/IGListAdapterUpdaterDelegate.h
@@ -21,6 +21,28 @@ NS_ASSUME_NONNULL_BEGIN
 NS_SWIFT_NAME(ListAdapterUpdaterDelegate)
 @protocol IGListAdapterUpdaterDelegate <NSObject>
 
+/**
+ Notifies the delegate that the updater is about to beging diffing.
+
+ @param listAdapterUpdater The adapter updater owning the transition.
+ @param fromObjects The items transitioned from in the batch updates, if any.
+ @param toObjects The items transitioned to in the batch updates, if any.
+ */
+- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater
+       willDiffFromObjects:(nullable NSArray <id<IGListDiffable>> *)fromObjects
+                 toObjects:(nullable NSArray <id<IGListDiffable>> *)toObjects;
+
+/**
+ Notifies the delegate that the updater finished diffing.
+
+ @param listAdapterUpdater The adapter updater owning the transition.
+ @param listIndexSetResults The diffing result of indices to be inserted/removed/updated/moved/etc.
+ @param onBackgroundThread Was the diffing performed on a background thread
+ */
+- (void)listAdapterUpdater:(IGListAdapterUpdater *)listAdapterUpdater
+        didDiffWithResults:(nullable IGListIndexSetResult *)listIndexSetResults
+        onBackgroundThread:(BOOL)onBackgroundThread;
+
 /**
  Notifies the delegate that the updater will call `-[UICollectionView performBatchUpdates:completion:]`.
 
diff --git a/Tests/IGListAdapterUpdaterTests.m b/Tests/IGListAdapterUpdaterTests.m
index da5a38d5..7eb14c01 100644
--- a/Tests/IGListAdapterUpdaterTests.m
+++ b/Tests/IGListAdapterUpdaterTests.m
@@ -814,6 +814,44 @@
     [self waitForExpectationsWithTimeout:30 handler:nil];
 }
 
+- (void)test_whenPerformingUpdate_thatCallsDiffingDelegate {
+    self.updater.experiments |= IGListExperimentBackgroundDiffing;
+
+    NSArray *from = @[
+        [IGSectionObject sectionWithObjects:@[] identifier:@"0"]
+    ];
+    NSArray *to = @[
+        [IGSectionObject sectionWithObjects:@[] identifier:@"0"],
+        [IGSectionObject sectionWithObjects:@[] identifier:@"1"]
+    ];
+    IGListToObjectBlock toBlock = ^NSArray *{
+        return to;
+    };
+
+    self.dataSource.sections = from;
+    [self.updater performReloadDataWithCollectionViewBlock:[self collectionViewBlock]];
+
+    id mockDelegate = [OCMockObject niceMockForProtocol:@protocol(IGListAdapterUpdaterDelegate)];
+    self.updater.delegate = mockDelegate;
+    [mockDelegate setExpectationOrderMatters:YES];
+    [[mockDelegate expect] listAdapterUpdater:self.updater willDiffFromObjects:from toObjects:to];
+    [[mockDelegate expect] listAdapterUpdater:self.updater didDiffWithResults:[OCMArg checkWithBlock:^BOOL(IGListIndexSetResult *result) {
+        return [result.inserts isEqualToIndexSet:[NSIndexSet indexSetWithIndex:1]]
+        && result.deletes.count == 0
+        && result.updates.count == 0
+        && result.moves.count == 0;
+    }] onBackgroundThread:YES];
+
+    XCTestExpectation *expectation = genExpectation;
+
+    [self.updater performUpdateWithCollectionViewBlock:[self collectionViewBlock] fromObjects:from toObjectsBlock:toBlock animated:NO objectTransitionBlock:self.updateBlock completion:^(BOOL finished) {
+        [expectation fulfill];
+    }];
+    waitExpectation;
+    [mockDelegate verify];
+}
+
+
 # pragma mark - preferItemReloadsFroSectionReloads
 
 - (void)test_whenReloadIsCalledWithSameItemCount_andPreferItemReload_updateIndexPathsHappen {